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A．By its thick layer of fat under its skin.
B．By moving frequently in the water.
C．By adjusting its blood temperature.
D．By taking in hot air.
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听力原文： Millions of years ago, whales lived on land and walked on four legs. Today, whales still have small bones that are the remains of their hind legs, but these bones can only be seen on the inside of the whale. No one knows why whales left the land to live in the water.
However, scientists can imagine that when the whales changed their environment, their bodies underwent a change—taking on a more fish-like appearance. This new form. offered less resistance to the water, enabling the whales to swim faster.
Despite their fish like form, whales are not fish. A whale will drown, just as a man will, if it stays under water too long. When a whale is under water, it closes its nostrils tightly and holds its breath. The air in its lungs becomes very hot and full of water vapor. When the whale rises to the surface and exhales, its hot breath produces a column of water vapor that rises high in the air. A man produces the same effect when he exhales warm air on a cold morning.
Whales are classified as mammals because they bear their young, rather than laying eggs, and because the mother whales give the babies milk. Like other mammals, whales have warm blood. Their blood stays at the same temperature, even when they move from hot to cold water. They keep warm in cold water because they have a thick layer of fat just under their skins. This fat is called blubber, and it is thicker on whales that spend their lives in cold water. Almost all land mammals, except man, have hair on their bodies to keep them warm, but whales, which have very few hairs, are kept warm by their fat.
How does a whale keep itself warm？
A．By its thick layer of fat under its skin.
B．By moving frequently in the water.
C．By adjusting its blood temperature.
D．By taking in hot air.
Because human anatomy does not change (except
over long periods of time), knowledge acquired a
century ago was still accurate today. Broad functions 【M1】 ______
of any part of the body, such as the skin, are dupli - 【M2】 ______
cated in different ways by organs. One can
eventually understand the entire body as a larger
system made up of smaller, interdependent system.
Cross-seciton of the skin reveals a top layer of 【M3】 ______
epidermis, or cuticle, followed by derma, and finally,
a subcutaneous cellular tissue. Sprouting through all 【M4】 ______
three layers are hairs, with hair follicles and erector
pili muscles embedded deep within the subcutaneous
tissue. Sweat (sudoriferous glands), fat cells, and
sebaceous glands are scattered throughout, however 【M5】 ______
papillae, which are conical and extremely sensitive,
can be found directly beneath the superficial layer.
The skin is the primary organ of the sense of
touch. It can also excrete substances as well as absorb 【M6】 ______
them, and it plays a vital role in regulating body
temperature and in protecting the tissue that lie 【M7】 ______
beneath it.
The epidermis has no veins or arteries and varies
considerably both in thickness and in the depth or
fineness of its furrows. On the palm, for example,
the skin is quite thick, or horny, and is marked by
deep furrows or lines. On the back of the hand,
however, the skin is thick, and has only a faint 【M8】 ______
network of lines crisscrossing it. The pigment found
in the epidermis gives whatever color there is to the
skin; this pigment is similar with that found in the retina 【M9】 ______
of the eye. One layer down, in the derma, there is
similar varietion in thickness, mostly to protect 【M10】______
underlying tissue.
【M1】
A layer of blubber approximately six inches thick protects the whale in Arctic waters.
A．Y
B．N
C．NG
The earth is made up of three major layers — a central core, probably metallic, some 4000 miles across, a surrounding layer of compressed rock, and to top it all a very thin skin of softer rock, only about 20 to 40 miles thick — that's about as thin as the skin of an apple, talking in relative terms.
The pressure on the central core is unimaginable. It has been calculated that at the centre it is 60 million pounds to the square inch, and this at a temperature of perhaps 10,000 degrees Fahrenheit. The earth's interior, therefore, would seem to be of liquid metal — and evidence for this is given by the behavior. of earthquake.
When an earthquake occurs, shock waves radiate from the centre just as waves radiate. outwards from the point where a stone drops into a pond. And these waves pulsate through the earth's various layers. Some waves descend vertically and pass right through the earth, providing evidence for the existence of the core and an indication that it is fluid rather than solid. Thus, with their sensitive instruments, the scientists who study earthquakes, the seismologists, can in effect X-ray the earth.
Iceland is one of the most active volcanic regions of the world. And it was to Iceland that Jules Verne sent the hero of his book A Journey to the Centre of the Earth. This intrepid explorer clambered down the opening of an extinct volcano and followed its windings until he reached the earth's core. There he found great oceans, and continents with vegetation. This is conception of a hollow earth we now know to be false. In the 100 years since Jules Verne published his book, the science of vulcanology, as it is called, has made great strides. But even so the deepest man has yet penetrated is about 10,000 feet. This hole, the Robinson Deep mine in South Africa, barely scratches the surface; so great is the heat at 10,000 feet that were it not for an elaborate air-conditioning system, the miners working there would be roasted. Oil borings down to 20,000 feet have shown that the deeper they go, the hotter it becomes.
The temperature of the earth at the centre is estimated to be anything between 3,000 and 11,000 degrees Fahrenheit. Some scientists believe that this tremendous heat is caused by the breaking-down of radio-active elements, which release large amounts of energy and compensate for the loss of heat from the earth's surface. If this theory is correct, then we are all living on top of a natural atomic powerhouse.
The outer layer of the earth is compared to the skin of an apple because ______.
A．it is about 20 to 40 miles thick
B．it is thin in proportion to the earth's mass
C．it is softer than the central core
D．it is thinner than the surrounding layer
A、Thick egg shell
B、Ascaroside layer
C、Protein membrane
D、Fertilization membrane
A．problems of space travel
B．scientific methods in space exploration
C．the importance of Venus to the earth
D．conditions on Venus
New York City has had several London type smog since 1950. Each time there were from 100 to 400 deaths caused by the smog.
In all the killer smog, factories and homes poured smoke and fumes into the air from the furnaces. The chemical fumes combined with the water-droplets in the fog to form. harmful substances. These substances caused the illness of those who breathed the polluted air.
Usually, such harmful fumes rise into the upper air and are blown away by the wind. But sometimes, there is an unusual weather condition called a temperature inversion. A layer of cold air remains near the ground as smoke and fumes pour into it. This is covered by an upper layer of warm air that acts like a lid. It prevents the polluted cooler air rising. The harmful fumes piles up and make people iii. These fumes contain sulfur dioxide, soot particles, and other chemicals. The smog may be so thick that airports are closed and chains of collisions occur on the highways.
Another type of smog occurs in Los Angeles. Here the weather may be clear and sunny, but stinging eyes and dry coughs show that harmful chemicals fill the air. The smog is due to invisible gases, mostly from automobile exhausts. Because these chemicals are changed by the sun up in the air, Los Angeles smog is called Photochemical smog. It contains automobile exhaust fumes and nitrogen oxides changed by the sun' s rays. Added to these are sulfur dioxide and other fumes from factories of oil refineries. Photochemical smog is found in many large cities all over the world.
Killer smog doesn' t happen very often, fortunately. But in many large cities, a combination of automobiles exhaust fumes, home furnace smoke, and factory waste gases pours into the air. This may also happen in the suburbs in the country, where large factories have been built. A number of harmful substances have affected the health of the population.
All of the following together form. smog Except ______ .
A．smoke and fumes
B．snow
C．water drops
D．fog
Every year thousands of grey whales make the longest migration of any animal, traveling 7,000 miles each way between the Arctic and Baja, California. The grey whales spend the long summer days in their Arctic feeding grounds in the Bering Sea between Alaska and Russia. Unlike a fish, the whale is warm-blooded and must therefore maintain a relatively high internal body temperature. In the cold Arctic waters the grey whale is protected by an outer layer of blubber which averages six inches in thickness. Other whales such as the Greenland Night whale have been found with a two-foot thick layer of blubber covering their bodies.
2. During these summer months, in the Arctic the grey whales fatten themselves by consuming enormous quantities of small shrimp-like animals called amphipods. Recent observations of a young grey whale, Gigi Ⅱ, held in captivity at Sea World in San Diego during 1971 and 1972, suggest that the grey whale feeds by sweeping its enormous head over the bottom. The amphipods on which it feeds are either stirred off the bottom or leap off the bottom to escape. These animals and the surrounding water are sucked into the whale&39;s mouth. As the water is expelled from the mouth, it passes through coarse baleen fibres. The small animals are trapped and swallowed.
3. In October as the days get shorter and ice begins to form. over the Arctic feeding grounds, the California grey whale begins its long journey south to the warm waters of Baja, California. During this three-month long trip the whales travelling in groups stay close to the shore of North America, swimming both day and night and averaging abut 100 miles per day.
4 During the trip south the grey whales that are sexually mature, at least three years old, and not pregnant already, form. mating groups. These groups are composed of three whales, two males and a female. The dominant male couples with the female while the second male is kept busy positioning the two whales on their sides facing each other and keeping them together during the sex act. This is no small job, since each whale can be fifty feet long and weigh forty tons.
5. During December and January the grey whales arrive at the warm lagoons along the coast of Baja, California. The whales swim miles inland along narrow shallow channels. These channels are the breeding grounds of the California grey whale. The calf has been gestating in the pregnant female for the last thirteen months, that is, since her last journey south. The expectant cow is aided in the birth of the calf by another female that acts as a midwife. At birth the calf sinks toward the sea floor. Being a mammal the whale must breathe at the surface. The midwife guides the baby whale to the surface for its first gulp of air. The calf then finds its mother&39;s nipples and rich whale milk is forced into its mouth. During the next two months the calf will grow twenty feet and double its weight.
6. In March the whales begin their long journey north to the Arctic. The newly-pregnant females leave first, following by the males and immature females. The last to leave the warm waters of Baja are the females and their calves. The whales arrive at their Arctic feeding ground in June. Many scientists believe that during this entire eight month long, 14,000 mile journey, the California grey whale does not feed at all!
Paragraph 3 ______
A. The Voyage Back B. An Arctic SummerC. Feeding Habits D. At the Breeding GroundsE. The Move SouthF. Mating
Paragraph 4 ______
A. The Voyage Back B. An Arctic SummerC. Feeding Habits D. At the Breeding GroundsE. The Move SouthF. Mating
Paragraph 5 ______
A. The Voyage Back B. An Arctic SummerC. Feeding Habits D. At the Breeding GroundsE. The Move SouthF. Mating
Paragraph 6 ______
A. The Voyage Back B. An Arctic SummerC. Feeding Habits D. At the Breeding GroundsE. The Move SouthF. Mating
A layer of blubber approximately six inches thick ______.
A. small shrimp-like animals called amphipods．B. protects the whale in Arctic waters.C. increase the circulation of its blood.D. two males and one female.E. leaves its Arctic feeding grounds,F. the surface of the water by a whale "midwife".
The whale feeds on______.
A. small shrimp-like animals called amphipods．B. protects the whale in Arctic waters.C. increase the circulation of its blood.D. two males and one female.E. leaves its Arctic feeding grounds,F. the surface of the water by a whale "midwife".
A mating group consists of ______.
A. small shrimp-like animals called amphipods．B. protects the whale in Arctic waters.C. increase the circulation of its blood.D. two males and one female.E. leaves its Arctic feeding grounds,F. the surface of the water by a whale "midwife".
The newly-born whale is assisted to _______.
A. small shrimp-like animals called amphipods．B. protects the whale in Arctic waters.C. increase the circulation of its blood.D. two males and one female.E. leaves its Arctic feeding grounds,F. the surface of the water by a whale "midwife".
Whales
鲸
Whales are aquatic mammals belonging to order CetaceA．A few species live in fresh water, but most species live in the seA．They have a streamlined shape and a powerful tail to drive them forwarD．With its two large horizontal fins or flukes, the tail produces the driving force by beating strongly up and down. Flippers at the front are used for steering and balance. The hind limbs of whales have completely disappeared, apart from a few small bones inside the body. Body hair has also disappeared, giving whales a smoother outline and less resistance to water.Instead of hair, whales are insulated by a thick layer of fat, or blubber, under the skin. The blubber may be as much as 61 cm thick on some parts of the body. Besides protecting the animal against the cold, the blubber is an important food reserve.
Most of the best-known whales large creatures.For example, the blue whale reaches a length of more than 30 m.However, many whales, such as dolphins and porpoises, are small.Some are only 1.5 to 1.8 m long.
Whales live entirely in water.Sometimes, whales are stranded on the shore.Although they are air-breathing animals, they soon die because their great weight keeps them from expanding (opening out) the chest cavity.They can breathe easily when afloat, because the water supports most of their weight.
The bottle-nosed whale has been known to stay under water for about two hours.The sperm whale can dive down to depths of 500 fathoms.Such long and deep dives are unusual.Most dives last between 10 and 30 minutes.Whales have special mechanisms that help them to stay under water.When they breathe, they renew about nine-tenths of the air in their lungs.When human beings breathe in, only about one-fourth of the air is renewed.Whales therefore have a fairly large supply of fresh air to start with.They also have an additional oxygen supply in the muscles, where air is loosely held in combination with a pigment called myohaemoglobin.Another thing that helps whales hold their breath for long periods of time is their low sensitivity to carbon dioxide in the blood.(It is the carbon dioxide building up in human blood that affects the brain and makes the human being take another breath.)
When a whale surfaces to renew its air supply, it needs only to push the top of its snout out of the water.This is because the nostril or blowhole is at the top of the heaD．The expelled air is forced out strongly to form. the spout or blow.
Living whales are divided into two groups—tooth whales and whalebone whales.Tooth whales, which include most species, generally have many conical teeth and eat mainly squids and fishes.The killer whale feeds on seals.One African river dolphin feeds mostly on plants.Other tooth whales include the narwhal and the sperm whale.
Whalebone whales have no teeth.Their mouths contain huge comblike fringes of baleen or whalebone.This horny substance is usually black.All whalebone whales feed by straining small animals from the water.The mouth is filled with water and the water is then forced out through the fringes by the tongue.The animals caught in the baleen are swept into the stomach by the tongue. All whalebone whales are large animals, which are usually found in cold seas.They include the blue whales, the right whales, and the rorquals.
The future of many of the larger kinds of whales is uncertain. Whalers have killed so many blue, bowhead, humpback, and right whales that those species are threatened with extinction. Overhunting has also greatly reduced the number of fin and sei whales.Also, if the human population does not stop increasing, people may have to compete with whales for food in the seA．Some nations have begun fishing for krill.Krill is the chief food of wha
A．good bodily resistance to water
B．only a few small bones inside the body
C．neither hind limbs nor body hair
D．a thick layer of fat under the skin
Rainforests
Tropical rainforests are the most diverse ecosystem (生态系统) on Earth, and also the oldest. Today, tropical rainforests cover only 6 percent of the Earth's ground surface, but they are home to over half of the planet's plant and animal species.
What Is a Rainforest？
Generally speaking, a rainforest is an environment that receives high rainfall and is dominated by tall tress. A wide range of ecosystems fall into this category, of course. But most of the time when people talk about rainforests, they mean the tropical rainforests located neat the equator.
These forests raceive between 160 and 400 inches of rain per year. The total annual rainfall is spread pretty evenly throughout the year, and the temperature rarely dips below 60 degrees Fahrenheit.
This steady climate is due to the position of rainforests on the golbe. Because of the orientation of the Earth's axis, the Northern and Southern hemispheres each spend part of the year tilted away from the sun. Since rainforests are at the middle of the globe, located near the equator, they are not especially affected by this change. They receive nearly the same amount of sunlight, and therefore heat, all year. Consequently, the weather in these regions remains fairly constant.
The consistently wet, warm weather and ample sunlight give plant life everything it needs to thrive. Trees have the resources to grow to tremendous heights, and they live for hundreds, even thousands, of years. These giants, which reach 60 to 150 It in the air, form. the basic structure of the rainforest. Their top branches spread wide in order to capture maximum sunlight. This creates a thick canopy (树冠) level at the top of the forest, with thinner greenery levels underneath. Some large trees grow so tall that they even tower over the canopy layer.
As you go lower, down into the rainforest, you find less and less greenery. The forest floor is made up of moss, fungi, and decaying plant matter that has fallen from the upper layers. The reason for this decrease in greenery is very simple: The overabundance of plandts gathering sunlight at the top of the forest blocks most sunlight from reaching the bottom of the forest, making it difficult for robust plants to thrive.
The Forest for the Trees
The ample sunlight and extremely wet climate of many tropical areas encourage the growth of towering trees with wide canopies. This thick top layer of the rainforest dictates the lives of all other plants in the forest. New tree seedlings rarely survive to make in to the top unless some older trees die, creating a "hole" in the canopy. When this happens, all of the seedlings on the ground level compete intensely to reach the sunlight.
Many plant species reach the top of the forest by climbing the tall trees. It is much easier to ascend this way, because the plant does's have to form. its own supporting structure.
Some plant species, called epiphytes, grow directly on the surface of the giant tress. These plants, which include a variety of orchids and ferns, make up much of the understory, the layer of the rainforest right below the canopy. Epiphytes are close, enough to the top to receive adequate light, and the runoff from the canopy layer provides all the water and nutrients (养分) they need, which is important since they don't have access to the nutrients in the ground.
tranglers and Buttresses
Same epiphytes eventually develop into stranglers. They grow long, thick roots that extend down the tree trunk into the
A．Y
B．N
C．NG
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