【正确答案】 D

【答案解析】[听力原文]
If someone asked you, "What color is the sky?" I expect you would answer "Blue". I am afraid that you would be wrong. The sky has no color. When we see blue, we are looking at blue sunlight. The sun is shining on little bits of dust in the air.
There is air all around the earth. We couldn"t breathe without air. Airplanes couldn"t fly without air. They need air to lift their wings. Airplanes cannot fly very high because as they go higher the air gets thinner. If we go far enough away from the earth, we find there is no air.
What is the sky? The sky is space. In this space there is nothing except the sun, the moon and all the stars.
The moon is about 384,000 kilometers away from the earth. An airplane cannot fly to the moon because the air reaches only 24.0 kilometers. Then there is no air. But rockets can fly even when there is no air.
You may ask, "How does a rocket fly?" If you want to know, get a balloon and then blow it up until it is very big. Don"t tie up the neck of the balloon. Let it go. The balloon will fly off through the air very quickly. The air inside the balloon rushes out through the neck of the balloon and this pushes the balloon through the air. It doesn"t need wings like an airplane.
This is how a rocket works. It is not made of rubber like a balloon, of course, it is made of metal. The metal must not be very heavy but it must be very strong. There is gas inside the rocket which is made very hot. When it rushes out the end of he rocket, the rocket is pushed up into the air and flies out into space.