place"发生"。

　　16．A.water B．money

　　C．food D．the earth

　　解析：选C　由前文中"Crops are ruined."，可知，国与国之间会为争夺粮食而战。

　　17．A.on the moon B．on the comet

　　C．in the ocean D．on the earth

　　解析：选D　句意：一年后地球上仅仅存留着一千万人。

　　18．A.be true B．happen

　　C．hit the earth D．destroy the earth

　　解析：选B　此句意为"这种事情真的会发生吗？"而非"这种事情可能是事实吗？"；因为it指这种事情，而不是该彗星，所以C、D两项都不对。

　　19．A.have been B．had been

　　C．were D．would be

　　解析：选C　句意：恐龙曾经在地球上生活过1.6亿多年。并没有延续到现在，所以不能用现在完成时态；另外，shows是现在时态，所以答案也不能用过去完成时态。

　　20．A.day B．climate

　　C．earth D．weather

　　解析：选B　句意：恐龙不能度过这样寒冷的气候。climate"气候"；weather常指短期的天气变化，故选B。

　　Ⅱ.短文改错

　　Dear Jane，

　　Glad to receive your letter. However, I'm terribly sorry to hear that you don't do good in maths and have lost interest with schoolwork. In my opinions, maths is difficult for many students, so there was no need to feel too bad. At this moment, you should cheer up and find ways to reduce your anxiety. Why not to go on an outing with your friends or listening to your favorite music? You can talk with the teachers you trust most, but they may give you some advice that can help you to improve. Probable it's time for you to explore new learning method. Anyway, I hope you can rebuild our self­confidence soon!

　　Yours，

　　Li Hua

　　答案：第二句：good→well; with→in

第三句：opinions→opinion; was→is