问题补充：
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 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. 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 perhaps 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 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.
【小题1】A comet is like .A．sunB．moonC．sunlightD．the earth【小题2】A large part of a comet is .A．water and rock B．water frozen into pieces of ice and mixed with ironC．ice, iron and rock dust D．only a few big pieces of rock【小题3】Maybe many people .A．haven’t seen any cometsB．have seen all cometsC．have seen a comet at daytimeD．have seen a comet【小题4】Some comets keep coming back .A．at any timeB．at noonC．at regular timesD．at daytime【小题5】Halley’s Comets came back .A．in 1990B．in 1980C．in 1986D．in 1989D
答案：
(答案→)D
解析：短文大意：本文介绍了有关彗星的知识。彗星有时看起来像个明星。就像一个行星，一颗彗星本身不发光。它是在反射阳光。如同地球一样，彗星绕着太阳转，但它比地球的旅行轨道更长。如果彗星不是一颗恒星，它是什么呢？短文叙述了一些科学家的观点。
【小题1】细节理解题。根据Like the earth, a comet goes round the sun, but…可知选D。
【小题2】细节理解题。根据…is water frozen into pieces of ice and mixed with iron and rock dust and perhaps a few big pieces of rock.这句话即能得出答案C。
【小题3】细节理解题。由第五段的首句Many people perhaps have seen a comet.可知选D。
【小题4】细节理解题。根据Some comets move out of our sight and never come back. Others keep coming back at regular times.一句可知选C。
【小题5】细节理解题。哈雷彗星每七十六年才能看到一次。再结合…the last time it came close to the sun and the earth was in the year 1986.这句话的意思，即可得到答案C。
