阅读下面短文，把方框中的句子还原到文中，然后完成第五小题。（每题1分，共5 分）
If you look at the sky one night and see something moving and shining that you have never seen before, it might be a comet (彗星).
　　A comet sometimes looks like a star.  ________ It shines from the sunlight it reflects (反射). Like the earth, a comet goes round the sun, but on a much longer path (轨道) than the earth travels.
If a comet isn’t a star, what is it then?
　  Some scientists think that a large part of a comet is water frozen into pieces of ice and mixed with iron and rock dust and perhaps a few big pieces of rock. __________ These clouds, together with the dust, form a long tail.
Many people perhaps have seen a comet. __________ .There may be millions of comets, but only a few come close enough for us to see.
An Englishman named Edmund Halley, who lived from 1656 to 1742, found out a lot about the paths that comets take through the sky.  __________  . Others keep coming back at regular times. A big comet that keeps coming back was named after Halley because he was the one who worked out when it would come back again. Maybe you have ever seen Halley’s Comets because the last time it came close to the sun and the earth was in the year 1986. Then people all over the world were outside at night to look at it. You will probably be able to see Halley’s Comets when it comes near the earth again.

A. However no one knows how many comets there are. B. Some comets move out of our sight and never come C. Like a planet, a comet has no light of its own. D. When sunshine melts (融化) the ice in the comet, great clouds of gas go trailing after it.

Which of the following is not true?

A．A large part of a comet is ice, iron and rock dust

B．Some comets keep coming back at any time

C．Halley’s Comets came back in 1986

D．Maybe many people have seen a comet

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