north into California and all around the Pacific Ocean. The cities of Los Angeles, San Francisco and Tokyo are completely 11 by earthquakes. Millions of people in the 12 half of the earth are already dead, and the 13 won't be safe for long. Because of the explosions, the sun is 14 by clouds of dust, and temperatures around the world fall to almost zero. Crops are ruined. The sun won't be seen again for many years. Wars 15 as countries fight for 16 . A year later, no more than 10 million people remain 17 .

　　Could it really 18 ？ In fact, it has already happened more than once in the history of the Earth. Science shows that dinosaurs (恐龙) 19 on the Earth for over 160 million years. Then 65 million years ago they suddenly disappeared. Many scientists believe that the Earth was hit by a piece of heavenly object. The dinosaurs couldn't live through the cold 20 that followed and they died out. Will we meet the same end?

　　1．A.attack　　　　　　　 B．hit

　　C．beat D．damage

　　解析：选B　彗星应该是"击中"地球，故应该是hit"击中；袭击"。beat意为反复的"打击"；attack"攻击"；damage"毁坏"。

　　2．A.piece B．comet

　　C．part D．half

　　解析：选A　指两块中的一块进入大气层。a piece与上一段中的two pieces相照应。

　　3．A.air B．environment

　　C．situation D．atmosphere

　　解析：选D　彗星碎块进入大气层。所以应用atmosphere。air"空气"；environment"环境"；situation"情况"。

　　4．A.rest B．other

　　C．remaining D．half

　　解析：选C　该彗星石的一部分已经毁灭，剩下的部分和地球相撞。rest不能作定语。只能用the rest of sth.。

　　5．A.sound B．voice

　　C．earth D．air

　　解析：选A　以两百倍于声速的速度才符合科学常识。

　　6．A.burns B．destroys

C．harms D．boils