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  3. 1. Why do airplanes take longer to fly west than east? It can take five hours to go west-east from New York(NY) to London bu

1. Why do airplanes take longer to fly west than east? It can take five hours to go west-east from New York(NY) to London bu

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问题     1. Why do airplanes take longer to fly west than east?
    It can take five hours to go west-east from New York(NY) to London but seven hours to travel east-west from London to NY. The reason for the difference is an atmospheric phenomenon known as the jet(喷射) stream. The jet stream is a very high altitude wind which always blows from the west to the east across the Atlantic. The planes moving at a constant air speed thus go faster in the west- east direction when they are moving with the wind than in the opposite direction.
    2. What would happen if the gravity on Earth was suddenly turned off?
    Supposing we could magically turn off gravity. Would buildings and other structures (建筑物) float away? What happened would depend on how strongly the things were attached to the Earth, The Earth is moving at quite a speed, moving at over a thousand miles per hours. If you turn something around your head on a string(细绳) , it goes around in a circle until you let go of the string. Then it flies off in a straight line. ’ Switching off’ gravity would be like letting go of the string. Things not attached to the Earth would fly off in a straight line. People in buildings would suddenly shoot up-wards at a great speed until they hit the ceiling. Most things outside would fly off into space.  
It can be inferred that without gravity______.
选项 A、buildings and other structures would float away
B、trees and buildings would not easily fly off
C、something around your head would not fly away
D、everything outside buildings would fly off into space
答案B
解析 第二段的标题的意思就是：地心引力突然消失了，会出现什么情况。根据本段的第三句，可知地球引力消失对物体的影响取决于物体本身对地球的依附程度。再由本段的倒数第三句可知，不依附于地球的物体会以直线形式飞走。由此可以推知依附地球的物体不易飞走。故B是正确答案。
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