Is the sky blue? The sky has no colour. We know that there is air around the world. When planes fly，they need air to lift their wings(翅膀).Planes cannot fly very high because when they go higher，the air gets thinner. If we go up about l 200 kilometers from the earth，we find there is no air.

Perhaps we can answer some of our questions now. The sky is space. In this space there is

only the sun，the moon and all the stars.

根据短文内容选择正确答案:

1.What is the sky?(　)

A. It’s the clouds.　　　　　　　　　　    B. It's space.

C. It’s air.　　　　　　　　　　    D. It’s nothing.

2.They sky________.(　)

A. is blue　　　　　　　　　　    B. is white

C. is black　　　　　　　　　　    D. has no colour

3.A plane cannot fly very high because________.(　)

A. the air becomes thinner

B. the flying machine is not good

C. people Will be afraid if the planes fly too high

D. it is not necessary for planes to fly so high

4.If we go up about l 200 kilometers from the earth，we find________.(　)

A. there is more air　　　　　　　　　　    B. there is 1ess air

C. there is nothing but air　　　　　　　　　　    D. there is no air

5.In space there is________.(　)

A. nothing　　　　　　　　　　    B. air everywhere

C. everything　　　　　　　　　　    D. only the sun. the moon and all stars