单项选择题

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
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单项选择题
Air moves under such conditions that______.
A．there is air pressure
B．the air is heavy
C．air pressure doesn't remain the same all the time
D．air comes up and down
单项选择题
According to the passage, we can conclude that in some areas if farmers who grow grapes light fires in the early morning, that is because the farmers want to______.
A．drive away warm air
B．prevent cold air from coming to harm their plants
C．cause more wind
D．stop warm air running away
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