A、A正确答案
B、B正确答案
C、C正确答案
D、D E正确答案
第1题
Air is a gas that expands (膨胀) when heated, gets lighter, and moves upward. When air is
cooled, it gets heavier, sinks close to the earth's surface, and flows like water in a great river. As warm air rises, cold air rashes to take its place. Thus winds originate (起源). Tile winds that blow high above us are caused by the warmer air running away from colder air. The wind we feel near the earth's surface is the heavy colder air trying hard to catch the warmer air. Changes in temperature cause the air to move. And of course there are many changes, so air movements are taking place practically all the time.
The first paragraph mainly tells us______.
A.why we don't feel air
B.why atmosphere is important to us
C.why there is air surrounding us
D.why there is air pressure
第2题
A.Because the water pressure is greater than air pressure.
B.Because the first Comets crashed in the water.
C.Because there is less damage when the explosion takes place under water.
D.Because it is the only way available for engineers to find out which part has cracked.
第3题
【M1】
第4题
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