题目内容：

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. Like a planet, a comet has no light of its own. It shines from the sunlight it reflects (反射). Like the earth a comet goes around the sun, but on a much longer path 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 (冻) into pieces of ice and mixed with iron and rock dust and perhaps a few big pieces of rock. When sunshine melts (融化) the ice in the comet, great clouds of gas go trailing after it. These clouds, together with the dust, form a long tail.

   Many people have seen a comet. However, no one knows how many comets there are. 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. Some comets move out of our sight and never come back. Others keep coming back at regular times. A big comet that keeps coming back was named after Halley comet, 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 comet when it comes near the earth again.

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.A comet is like.

A. the sun     B. the moon

C. sunlight    D. the earth

2.A large part of a comet is.

A. water and rock  

B. water frozen into pieces of ice and mixed with iron and rock dust and perhaps a few pieces of rock

C. ice, iron and rock dust 

D. only a few big pieces of rock

3.Many people.

A. haven’t seen any comets

B. have seen all comets

C. have seen a comet at daytime 

D. have seen a comet

4.Some comets keep coming back.

A.at any time

B.at noon

C.at regular times 

D.at daybreak (拂晓)

5.When did Halley’s comet come close to the sun and the earth last time?

A. In 1656.     B. In 1742.

C. In 1986.    D. In 1996.