Rockets in the Sky

If someone askedyou,"What color is the sky?"I expect that you wouldanswer,"Blue."I am afraid that you would be wrong.The sky has nocolor.When we see blue,we are

looking at bluesunlight.The sunlight is shining on little bits of dust in the air.

We know that thereis air all around the world.We could not breathe without air.Airplanes couldnot fly without air.They need air to lift their wings.Airplanes cannot fly very

high because as theygo higher the air gets thinner.If we go far enough away from the earth,we findthere is no air.

What is the sky?Thesky is space.In this space there is nothing except the sun,the moon and all thestars. Scientists have always wanted to know more about the other worlds

in the space.Theyhave looked at them through telescopes and in this way they have found out a greatdeal.The moon is about 384 ,000 kilometers away from the earth.An

airplane cann't flyto the moon but there is a thing that can fly even when there is no air. Thisis rocket.

I am sure that youare asking,"How does a rocket fly?"If you want to know,get a balloonand then blow it up until it is quite big.Do not tie up the neck of theballoon.Let go!

The balloon will flyoff through the air very quickly.The air inside the balloon tries to get out.Itrushes out through the neck of the balloon and this pushes the balloon through

the air.It does notneed wings like an airplane.

This is how a rocketworks.It is not made of rubber（橡胶）like a balloon,of course.It is made of metal. The metal must not beheavy but it must be very strong.There is gas

inside the rocketwhich is made very hot. When it rushes out of the end of the rocket,the rocketis pushed up into the air.

Rockets can fly farout into space.Rockets with men inside them have already reached themoon.Several rockets,without men inside them,have been sent to other worlds

much fartheraway.One day rockets may be able to go anywhere in the space.When an airplaneflies too high,______.

A.the air will betoo thin to support its wings

B.the air willbecome thicker

C.the air will exertpressure on it

D.the air willdisappear in no time