阅读理解。

     What is the sky? Where is it? How high is it? What lies above the sky? I am sure you have often asked

these questions. They are very difficult to answer, aren't they?

     If someone asks you:"What color is the sky?" I think maybe you will answer"Blue". I am afraid you are

wrong. The sky has no colors. When we see blue, it is the sunlight that is shining on little bits of dust in the

air.

     Is the sky full of air? I am sure you have asked this question, too. We know that there is air all around the

earth. Planes can't fly without air. They need air to lift their wings. Planes can't fly very high because as they

go higher, the air gets thinner. If we go too high up in the sky, we find there is no air.

     Perhaps you can answer some of the questions now. What is the sky? Nothing. Where is it? It is all around

the earth. The sky is a part of space.

1. What color is the sky according to the writer?

A. Blue.

B. White.

C. Black.

D. Colorless.

2. What is in the sky?

A. It's empty.

B. It's full of air.

C. It has clouds.

D. It has rains.

3. What is the meaning of the underlined word "dust"?

A. 灰尘

B. 乌云

C. 空气

D. 雨滴