题目内容
（请给出正确答案）
A、silica
B、calcium
C、carbonate
D、iron oxides
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更多“Desert dust containscommon crustal minerals,such as .”相关的问题
A.barren
B.bound
C.radiant
D.robust
According to the passage, which of the following statements is true？,
A．Our galaxy contains great interstellar dust clouds.
B．Near misses of bodies smaller than our own planet could be disastrous.
C．The probability of collision with a large astronomical body is very high.
D．The chances of anyone actually being hit by missiles are very high.
听力原文： Lecturer: In the last lecture, we looked at the adverse effects of desert dust on global climate. Today we're going to examine more closely what causes dust storms and what other effects they can have. As you know, dust storms have always been a feature of desert climates, but what we want to focus on today is the extent to which human activity is causing them. And it is this trend that I want to look at, because it has wide-ranging implications. So, what are these human activities？ Well, there are two main types that affect the wind erosion process, and thus the frequency of dust storms. There are activities that break up naturally wind-resistant surfaces such as off-road vehicle use and construction and there are those that remove protective vegetation cover from soils, for example, mainly farming and drainage. In many cases the two effects occur simultaneously which adds to the problem.
Let's look at some real examples and see what I'm talking about. Perhaps the best-known example of agricultural impact on desert dust is the creation of the USA's 'dust bowl' in the 1930s. The dramatic rise in the number of dust storms during the latter part of that decade was the result of farmers' mismanaging their land. In fact, choking dust storms became so commonplace that the decade became known as the 'Dirty Thirties'.
Researchers observed a similar, but more prolonged, increase in dustiness in West Africa between the 1960s and the 1980s when the frequency of the storms rose to 80 a year and the dust was so thick that visibility was reduced to 1,000 metres. This was a hazard to pilots and road users. In places like Arizona, the most dangerous dust clouds are those generated by dry thunderstorms. Here, this type of storm is so common that the problem inspired officials to develop an alert system to warn people of oncoming thunderstorms. When this dust is deposited it causes all sorts of problems for machine operators. It can penetrate the smallest nooks and crannies and play havoc with the way things operate because most of the dust is made up of quartz which is very hard. Another example - the concentration of dust originating from the Sahara has risen steadily since the mid-1960s.
This increase in wind erosion has coincided with a prolonged drought, which has gripped the Sahara's southern fringe. Drought is commonly associated with an increase in dust-raising activity but it's actually caused by low rainfall which results in vegetation dying off.
One of the foremost examples of modern human-induced environmental degradation is the drying up of the Aral Sea in Central Asia. Its ecological demise dates from the 1950s when intensive irrigation began in the then Central Asian republics of the USSR. This produced a dramatic decline in the volume of water entering the sea from its two major tributaries. In 1960, the Aral Sea was the fourth-largest lake in the world, but since that time it has lost two-thirds of its volume, its surface area has halved and its water level has dropped by more than 216 metres. A knock-on effect of this ecological disaster has been the release of significant new sources of wind-blown material, as the water level has dropped.
And the problems don't stop there. The salinity of the lake has increased so that it is now virtually the same as sea water. This means that the material that is blown from the dry bed of the Aral Sea is highly saline. Scientists believe it is adversely affecting crops around the sea because salts are toxic to plants.
This shows that dust storms have numerous consequences beyond their effects on climate, both for the workings of environmental systems and for people living in drylands ...
SECTION 4 Questions 31-40
Questions 31-32
Complete the notes using NO MORE THAN THREE WORDS for each answer
Main focus of lecture: the impact of 【31】______ on the occurrence of dust st
Section B
Directions: In this section, you will hear 3 short passages. At the end of each passage, you will hear some questions. Both the passage and the questions will be spoken only once. After you hear a question, you must choose the best answer from the four choices marked A, B, C and D.
听力原文： Would the world really be so much better off if there were no dust？ The answer is in some ways, yes, in some ways, no. What is dust anyway？ It consists of particles of earth, or other solid matter, which are light enough to .be raised and carried by the wind. Where do these particles come from？ They might come from dead plants and animal matter, from sea salt, from desert or volcano sand and from ashes. For the most part, dust is not a very desirable or beneficial thing. But in one way, it helps make the world more beautiful. The lovely colors of the dawn depend to a great extent on the amount of dust that is present in the air. Particles of dust in the upper air reflect the sun's rays. This makes its light visible on earth an hour or two after sunset. But different colors which make up the sun light are bent .at different angles as they are reflected by the dust and water steam particles. Sunsets are red, because these particles bent the red rays of the sun in such a way that they are the last rays to disappear from view. Another useful function of dust has to do with ram. The vapor water in the air would not become a liquid very readily, if it did not have the dust particles serving as centers for each drop of water. Therefore, clouds, mist, fog and rain are largely formed of an infinite number of moisture particles of dust.
(27)
A．Of course.
B．It depends.
C．Certainly not.
D．It is not mentioned.
Heather Price, a University of Washington doctoral student in chemistry, found that the amount of light reflected by the particles in the air was more than 550 percent greater than normal for that time of year. The mass of Asian air contained elevated levels of ail pollutants measured. Price said, "but the only thing that came close to being alarming was the level of particulate matter."
The haze that settled across the western part of the country was widely reported by the news media, and it was measured as far inland as the ski slopes of Aspen, Colo.
Readings on the western side of the Pacific came from the Aerosol Characterization Experiments, a project aimed at understanding how particles in the atmosphere affect Earth's climate. Additional measurements were taken in the same region at the same time under a project sponsored by the National Aeronautics and Space Administration.
Knowing the pollution was approaching Washington state, Price loaded sensing equipment aboard a rented Beechcraft on April 14 and flew to Neah Bay on the state's Northwest coast. Taking samples at various levels from 15,000 feet to 20, 000 feet in altitude, she monitored quantities of dust, ozone, carbon monoxide and hydrocarbons. "From my copilot's seat. the dust was thick enough to see with the naked eye." Price said.
Now she is trying to correlate her findings with those of the two research teams operating on the other side of the Pacific, where at one point the pollution plume was larger than Japan. The huge size of the cloud showed up clearly in satellite images that gave Price plenty of warning the haze was on its way. "You can see these two blobs coming out of the deserts of Mongolia and growing over Asia, then getting swept out over the ocean and finally setting over North America," she said. She intends to continue measuring air samples off the Washington coast and will be looking for air masses with evidence of pollution originating somewhere other than Asia. "We'd like to see if we can get a signature of pollution coming from Europe because computer models suggest that European sources also can be transported across the Pacific," she said. "However, we expect that sources in Europe will contribute less than Asian sources."
The haze of pollution mentioned in the first paragraph is a cloud ______.
A．of moisture over Calgary, Canada
B．developing over Pacific Ocean
C．of industrial pollutants
D．of desert dust and hydrocarbons
Droplets and ice crystals behave somewhat like dust in the air made visible in a shaft(束) of sunlight. To the casual observer, dust seems to act in a totally random fashion, moving about wildly without fixed direction. But in fact dust particles are much larger than water droplets and they finally fall. The cloud droplet of average size is only 1/2,500 inch in diameter. (78)It is so small that it would take sixteen hours to fall half a mile in perfectly still air, and it does not fall out of moving air at all. Only when the droplet grows to a diameter of 1/125 inch or larger can it fall form. the cloud. The average raindrop contains a million times as much water as a tiny cloud droplet. The growth of a cloud droplet to a size large enough to fall out is the cause of rain.
What is the main topic of the passage？
A．The mechanics of rain.
B．The climate of North America.
C．How gravity affects air current.
D．Types of clouds.
SECTION B PASSAGES
Directions: In this section, you will hear several passages. Listen to the passages carefully and then answer the questions that follow.
听力原文： What makes it rain.9 Rain falls from clouds for the same reason anything falls to Earth. The Earth's gravity pulls it. But every cloud is made of water droplets or ice crystals. Why doesn't rain or snow fall constantly from all clouds？ The droplets or ice crystals in clouds are exceedingly small. The effect of gravity on them is minute. Air currents move and lift droplets so that the net downward displacement is zero, even though the droplets are in constant motion.
Droplets and ice crystals behave somewhat like dust in the air made visible in a shaft of sunlight. To the casual observer, dust seems to act in a totally random fashion, moving about chaotically without fixed direction. But in fact dust particles are much larger than water droplets and they finally fall. The cloud droplet of average size is only 1/2500 inch in diameter. It is so small that it would take sixteen hours to fall a mile in perfectly still air, and it does not fall out of moving air at all. Only when the droplet grows to a diameter of 1/125 inch or larger can it fall from the cloud. The average raindrop contains a million times as much water as a tiny cloud droplet. The growth of a cloud droplet to a size large enough to fall out is the cause of rain and other forms of precipitation. This important growth process is called "coalescence".
What is the main topic of the passage？
A．The mechanics of rain.
B．The climate of North America.
C．How gravity affects air current.
D．Types of clouds.
Four seasons are characteristic of the Gobi: spring, summer, fall, and winter, with usually a false spring at the end of winter. These seasons are distinct, with extremes of temperature, as much as 150 between the hottest day in summer and the coldest day in winter.
Spring in the Gobi usually begins about the second week April. For 2 or 3 weeks there is a period of delightful weather, with warm, sunny days and not too much wind. But these are the days of false spring. About the first of May, the tail end of winter returns, and cold, blustery days of dustburdened winds are the rule then, until early or middle June. The latter part of June, for 2 or 3 weeks after the blowy end of winter is the real spring. It spreads its rather comfortable warmth over the desert, and occasional light rains help the desert grass to come along nicely.
July, or sometimes mid-June to mid-August is summer. Hot days are the rule, but the nights are cool. Wind and dust again govern the desert, but this is the season when hard rains, if they come at all, are most likely to dump water on the plains.
Fall usually may be recognized by the encouraging, bright days beginning in mid-August and lasting until mid-September or the first of October. This is the time of year when both men and beasts feel best in the Gobi. The clear air, bright sun, and frosty temperatures make you glad to be alive.
Winter comes with a rush anytime after the middle of September. One day you may be enjoying a pleasant temperature near the eighties. But suddenly the air cools. In a few hours the temperature has slipped below 50; and a little later cold rain changes to snow and blustering wind.
In this passage the author briefly describes ______.
A．the different seasonal changes
B．the effects of climatic change on msn and beasts
C．the Gobi as a terrible place to live in
D．the seasonal cycle of the Gobi
No two comets ever look identical, but they have basic features in common, one of the
most obvious of which is a coma. A coma looks like a misty, patch of light with one or more
tails often streaming from it in the direction away from the Sun.
At the heart of a comet's coma lies a nucleus of solid material, typically no more than
(5) 10 kilometers across. The visible coma is a huge cloud of gas and dust that has escaped
from the nucleus, which it then surrounds like an extended atmosphere. The coma can extend
as far as a million kilometers outward from the nucleus. Around the coma there is often an
even larger invisible envelope of hydrogen gas.
The most graphic proof that the grand spectacle of a comet develops from a relatively
(10) small and inconspicuous chunk of ice and dust was the close-up image obtained in 1986 by
the European Giotto probe of the nucleus of Halley's Comet. It turned out to be a bit like a
very dark asteroid, measuring 16 by 8 kilometers. Ices have evaporated from its outer layers
to leave a crust of nearly black dust all over the surface. Bright jets of gas from evaporating
ice burst out on the side facing the Sun, where the surface gets heated up, carrying dust
(15) with them. This is how the coma and the tails are created.
Comets grow tails only when they get warm enough for ice and dust to boil off. As a
comet's orbit brings it closer to the Sun, first the coma grows, then two distinct tails usually
form. One, the less common kind, contains electrically charged (i.e., ionized) atoms of gas,
which are blown off directly in the direction away from the Sun by the magnetic field of
(20) the solar wind. The other tail is made of neutral dust particles, which get gently pushed back
by the pressure of the sunlight itself. Unlike the ion tail, which is straight, the dust tail
becomes curved as the particles follow their own orbits around the Sun.
The passage focuses on comets primarily in terms of their
A．orbital patterns
B．coma and tails
C．brightness
D．size
Air pollution involves the release into the atmosphere【C1】______ gases, finely divided solids, or finely dispersed liquid aerosols at rates that【C2】______ the capacity of the atmosphere to dissipate them or to dispose【C3】______ them through incorporation into solid or【C4】______ layers of the biosphere. Air pollution【C5】______ a variety of causes, not all of which are【C6】______ human control. Dust storms in desert areas and smoke from forest and grass fires【C7】______ to chemical and particulate pollution of the air. Forest fires that swept the state of Victoria, in Australia, in 1939 caused【C8】______ air pollution in Queensland, more than 2,000 miles (3,000 kilometres) away. Dust blown from the Sahara has been【C9】______ in West Indian islands. The discovery of 【C10】______ in Antarctica, where they have never been used, suggests the【C11】______ to which aerial transport can carry pollutants from one place to another. Probably the most important natural【C12】______ of air pollution is volcanic activity , which at times【C13】______ great amounts of ash and toxic【C14】______ into the atmosphere. The eruptions of such volcanoes as Krakatoa, in the East Indies, Mt. St. Helens, in Washington, and Katmai, in Alaska, have been 【C15】______ to 【C16】______ climatic changes.
Air pollution may affect humans directly, causing a smarting of the【C17】______ or coughing. More indirectly, the effects of air pollution are experienced at【C18】______ distances from the source, as, for example, the fallout of tetraethy lead from urban automobile【C19】______ which has been observed in the oceans and on the Greenland ice sheet. Still【C20】______ directly experienced are the possible effects of air pollution on global climates.
【C1】
A．at
B．of
C．by
D．with
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