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　　Our sun is a star, and nine worlds (天体) move round it. Worlds like these are planets. 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 been anymore. The stars are too far away from us. Stars give out light, but the planets don't have any light of their own. So we can't see them. They are 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 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 known Bernard's Star for many years, and now we are sure it has a planet.

　　16. A star is a l arge body in the universe. It _________.

　　A. moves round our sun     B. has light of its own

　　C. can also be called a sun     D. both B and C

　　17. Which of the following is not true?

　　A. The earth is one of the sun's world's   B. There are millions of suns in the universe

　　C. The world's are very bright          D. some stars have planets

　　18. We can see the planets round our sun. But we can't see ________.

　　A. nine worlds in the universe      B. the planets round other stars

　　C. the satellites round the earth     D. other stars

　　19. Barnard's Star moves more quickly than ________.

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

　　20. How can people know that there is a planet 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[来源:Zxxk.Com]

　　C. The planet is next to our earth.

　　D. The planet is a red one.

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