题目内容
（请给出正确答案）
Oxygen is often stored as a liquid, although it is used () as a gas.
A、primarily
B、seldom
C、rarely
D、sometimes
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更多“Oxygen is often stored as a liquid, although it is used （) as a gas.A、primarilyB、seldomC”相关的问题
Which of the following statements is NOT true according to the report？
A．Workers made tunnels through ice.
B．Construction workers often use oxygen bottles to breathe.
C．The new railway will use ordinary trains.
D．The new line is to start operation in 2006.
What is the harmful effect of sulfur in a fuel？
A.It causes excessive smoking and soot at low firing rates
B.It doesn’t readily burn when combined with oxygen
C.It clogs fuel oil strainers more often
D.It forms a corrosive acid when mixed with water or water vapor
What does the passage tell us about firefighter Eric Velez？
A.He teaches Spanish in a San Francisco community.
B.He often teaches children what to do during a fire.
C.He travels all over America to help put out fires.
D.He provides oxygen masks to children free of charge.
【M1】
A．Scientists have found that an athlete"s heart requires a period of time to adjust to working at high altitudes.
B．Scientists have found that the body" s total volume of blood declines by as much as 25 percent at high altitudes.
C．Middle-distance runners who train at high altitudes sometimes lose races to middle-distance runners who train at sea level.
D．The performances of athletes in competitions at all altitudes have improved markedly during the past twenty years.
E．At altitudes above 5,500 feet, middle-distance runners often better their sea-level running times by several seconds .
【C1】______, more than 100,000 wildfires clear 4 million to 5 million acres of land in the U. S. every year. A wildfire moves at speeds of up to 23 kilometers an hour, consuming everything— trees, bushes, homes, even humans—in its【C2】______.
There are three conditions that need to be【C3】______in order for a wildfire to burn: fuel, oxygen, and a heat source. Fuel is any material【C4】______a fire that will burn quickly and easily, including trees, grasses, bushes, even homes. Air supplies the oxygen a fire【C5】______to burn. Heat sources help spark the wildfire and bring fuel to【C6】______hot enough to start burning. Lightning, burning campfires or cigarettes, hot winds, and even the sun can all provide【C7】______heat to spark a wildfire.
【C8】______often harmful and destructive to humans, naturally occurring wildfires play a positive role in nature. They【C9】______nutrients to the soil by burning dead or decaying matter. They remove diseased plants and harmful insects from a forest ecosystem (生态系统 ). And by burning【C10】______thick trees and bushes, wildfires allow sunlight to reach the forest floor, enabling a new generation of young plants to grow.
【C1】
A．After all
B．Above all
C．In sum
D．On average
【C1】______, more than 100,000 wildfires clear 4 million to 5 million acres of land in the U. S. every year. A wildfire moves at speeds of up to 23 kilometers an hour, consuming everything— trees, bushes, homes, even humans—in its【C2】______.
There are three conditions that need to be【C3】______in order for a wildfire to burn: fuel, oxygen, and a heat source. Fuel is any material【C4】______a fire that will burn quickly and easily, including trees, grasses, bushes, even homes. Air supplies the oxygen a fire【C5】______to burn. Heat sources help spark the wildfire and bring fuel to【C6】______hot enough to start burning. Lightning, burning campfires or cigarettes, hot winds, and even the sun can all provide【C7】______heat to spark a wildfire.
【C8】______often harmful and destructive to humans, naturally occurring wildfires play a positive role in nature. They【C9】______nutrients to the soil by burning dead or decaying matter. They remove diseased plants and harmful insects from a forest ecosystem (生态系统 ). And by burning【C10】______thick trees and bushes, wildfires allow sunlight to reach the forest floor, enabling a new generation of young plants to grow.
【C1】
A．After all
B．Above all
C．In sum
D．On average
For instance, some animals yawn to intimidate intruders on their territory. Fish and lizards are examples of this. Hippos use yawns when they want to resolve a quarrel. Observers have seen two hippos yawn at each other for as long as two hours before they stop quarreling.
As for social animals like baboons or lions--they yawn to set up the pecking order within social groups, and lions often yawn to calm social tensions. Sometimes these animals yawn for a strictly physiological reason--that is to increase oxygen levels. And curiously enough, when they yawn for a physical reason like that, they do what men do-they try to stifle the yawn by looking away or by covering their mouths.
What's the main topic of the monologue？
A．Different animals' yawns.
B．Human's yawn.
C．Fish's yawn.
D．Social animals' yawns.
【M1】
A typical clay soil is composed of approximately 60 percent actual clay, 20 percent silt, and 20 percent sand. The particles in a sandy soil are so fine that it tends to be compact and interferes with the oxygen supply for plant roots. Water has trouble entering this impervious soil, and runoff is very common during rainfalls.
A typical light sandy soil is composed of approximately 70 percent sand, 20 percent silt, and 10 percent clay. The particles in a sandy soil are comparatively large, permitting water to enter the soil and to pass through it so quickly that it often carries nutrients with it and dries out very rapidly. The texture of sandy soils is generally very difficult to modify because huge amounts of organic material must be added.
A typical loam soil is composed of approximately 40 percent sand, 40 percent silt, and 20 percent clay, making it an ideal garden soil. It is easily worked and retains water and nutrients, which are slowly absorbed by plant roots.
A typical adobe soil is a clay soil present in hot, dry areas of the country and is often very hard and cracked. It has all the disadvantages of a heavy clay soil and, being much drier, is more difficult to correct.
What is the author's main purpose in this passage？
A．To tell gardeners how to modify their soil.
B．To classify soil types on the basis of their composition.
C．To illustrate the effects of soil type on plant growth.
D．To show how water is absorbed by different soil.
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