叙述自然循环原理？

Our sun is a star, and nine worlds move round it. Worlds like these are planets (行星).
But there are other stars, other suns. Not only thousands of them, but millions of them. Do different stars have planets? We can see the planets round our own sun. But we haven’t seen any more. The stars are too far away from us. Stars give out (发出)light, but the planets don’t have any light of their own. So we can’t see them. They’re too far, and too dark.
Still, we can tell that some stars have planets. While a big planet goes round, it pulls its star to one side. And sometimes we can see this, Then we know that the star has a planet.
For example, Barnard’s Star（巴纳德星）is a small red star. And it is the quickest star in the universe. But sometimes it moves slower, and then quicker again. We have know Barnard’s Star for many years, and now we are sure it has a planet.
小题1:A star is a large body in the universe.it________.

A．moves round our sun	B．has light of its own
C．can also be called a world	D．both B and C

小题2:Which of the following is not true?

A．The earth is one of sun’s worlds	B．There are millions of suns in the universe.
C．The worlds are very bright.	D．Some stars have planets

小题3:Barnard’s Star moves more quickly than _______.

A．most stars	B．any other star
C．its planet	D．the planets round the sun

小题4:How can people know that there is a plante round Barnard’s Star?

A．Sometimes they see that the planet pulls the star to one side and makes it move slower .	B．The planet is shining.
C．The planet is next to our earth.
D．The planet is a red one.