If someone asks you "What color is the sky", I think your answer will be "blue". I'm afraid that you
are wrong. Because the sky has no color. 
     What's in the sky? Is the sky full of (充满) air? I'm sure that you have asked these questions. We all
know that there is air around the world. We can not live without air. Planes can't fly very high because
as we go higher, the air gets thinner (更稀薄). If we go far enough away the earth, we can find that there
is no air. The sky is space (太空). In the space there is nothing but the sun, the moon and the stars.
       People always want to know more about other worlds in space. They have looked at them through
telescopes (望远镜) and in this way they have known much. They know a lot about the moon now. but
they want to know more about space. I'm sure they will go farther and farther until they know all about it.
1. It's not really right _____. 
A. to answer questions about space  
B. to answer questions about the sky 
C. to say that the sky is blue        
D. to say that the sky has no color
2. _____ helps plane fly. 
A. The sky    
B. The air    
C. Space  
D. The sun
3. There is no air _____. 
A. around us    
B. around the eart  
C. in the sky
D. high enough in the sky
4. There is _____ in space. 
A. air                            
B. nothing 
C. nothing but the sun, the moon and the stars 
D. nothing or the sun, the moon and the stars
5. With telescopes people can know _____ in space. 
A. much    
B. nothing      
C. everything    
D. all

     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