题目内容：

Scientists have always wanted to know more about the other worlds in space.

   Years ago, they knew many facts about the moon. They knew how big it was and how far away it was from the earth. But they wanted to know more about it .They thought and thought. At last they found the only way to know more was to send men to the moon.

   The moon is about three hundred and eighty-four thousand kilometers away from the earth. A plane can not fly to the moon because the air reaches only 240 kilometers. Then there is no air. But something can fly even when there is no air. That is a rocket.

   How does a rocket fly? There is gas in the rocket. When the gas is made very hot inside the rocket, it will rush out of the end of the rocket, so it can make the rocket fly up into the sky.

   Rockets can fly far out into space. Rockets with men in them have already reached the moon. Some rockets without men in them have flown to other planets much farther away than the moon. One day rockets may be able to go to any place.

根据短文内容，从题中所给的A、B、C、D四个选项中，选择最佳答案。

1.What does the underlined word “worlds” refer to?

A. moon    B. planets    C. fields  D. sky

2.The moon is about   kilometers away from the earth.

A.384000      B.348000    C.3840   D.3480

3.A plane can’t fly to the moon because   .

A. it’s too far away  

B.it can’t fly without air

C. there is no water on the moon

D.it is too small

4.The hot gas in the rocket is used for   .

A. cooking food for the astronauts

B. keeping the man in the rocket warm

C. making the rocket fly up

D. keeping the air in the rocket fresh

5.Rockets without men in them have reached   .

A. another star

B. the sun

C. the moon

D. other planets of the sun