单选题 Dinosaurs were reptiles which became extinct about 65 million years ago. The most intriguing question about dinosaurs has always been " (21) did they die out?" There is no simple answer to this question, (22) many hundreds of scientists are studying the problem. They are not studying the extinction of the dinosaurs (23) , but the whole question of extinction. Many other plants and animals have (24) in the past, and it is important to understand (25) this happened. Having this information could help save many species that are (26) in the modern world. Humans are causing extinctions now, because of pollution and other damage (27) the environment. Maybe the dinosaurs can tell us how to save the earth today, (28) their extinction 65 million years ago! Some of the early dinosaur scientists, 100 years ago, thought the dinosaurs died out because the (29) changed, and they could not breathe. Others thought that the dinosaurs disappeared simply because they became too big.
They were (30) to move and could not find enough food (31) One theory is that a huge killer meteorite (32) the earth. Some scientists (33) that the extinction of dinosaurs was possibly due to rapid (34) of the planet's climate. Perhaps huge amounts of lava pours out of volcanoes in India. This sent up vast (35) of dust that blacked out the sun, and made the earth icy cold.

单选题 A. knocked B. hit C. collapsed D. crashed
【正确答案】 D
【答案解析】考查动词的用法。文中称有一种理论是一颗陨石撞击了地球。knock使碰撞；以打击，用力地碰；collapse倒坍，坍陷；crash突然猛烈地撞击，并伴有轰隆声。因此答案是crash。
单选题 A. expressed B. considered C. insisted D. held
【正确答案】 B
【答案解析】考查动词的用法。句中要表示科学家的一种看法。A项中的express有“表达”的意思；选项consider“认为，以为”，可以后接that从句；选项insisit“主张，坚持”，常与on连用，表示“坚持某个看法”。
单选题 A. cooling B. colding C. warming D. heating
【正确答案】 A
【答案解析】下文提到：火山灰遮住了太阳，使得地球变得冰冷。因此本句中说到的气候变化应是地球变冷。
单选题 A. amounts B. crowds C. clouds D. spread
【正确答案】 B
【答案解析】cloud of dust云状物(如烟雾、尘雾等)，例如：The freight truck caused a cloud of dust as it went down the dirt road．运货卡车驶过那条肮脏的道路时卷起了一片尘土。
单选题 A. when B. why C. how D. /
【正确答案】 C
【答案解析】本题涉及到对文章下文的理解。下文提到多个观点说明恐龙灭绝的原因，而第1句就明确了恐龙灭绝的时间，因此本句中应该选择how来表达大家的疑问。
单选题 A. as B. because C. even if D. even though
【正确答案】 D
【答案解析】考查上下句逻辑关系和副词的词义。选项D even though“即使，尽管”，强调不管事实上如何，对既成事实的否定，符合题意。even if“即使，尽管”虽然也有转折之意，但更多的是对将要发生的情况的假设。
单选题 A. themselves B. by themselves C. alone D. only
【正确答案】 D
【答案解析】下文提到科学家想通过研究恐龙的灭绝找出拯救现代濒临灭绝的动植物的方法。联系上下文可以肯定答案是only“仅仅，只不过”。
单选题 A. wiped out B. eliminated C. been extincted D. died out
【正确答案】 D
【答案解析】这里的die out是上文句中的词语复现，表示“消失，灭绝”。extinct本身是个形容词，应使用这样的结构：have been extinct。
单选题 A. how and why B. when and why C. how and when D. why and when
【正确答案】 D
【答案解析】考查对文章的理解。科学家研究的问题重点是物种灭绝的原因，而不是时间。因此凡是涉及到时间when的选项都是错误的。因此答案是A。
单选题 A. at danger B. under threat C. dangerous D. threatening
【正确答案】 B
【答案解析】本句话的意思是：掌握了这些信息，科学家就可以帮助拯救现今面临灭绝危险的物种了。面临危险要用词组under threat。
单选题 A. to B. for C. with D. in
【正确答案】 A
【答案解析】考查词语搭配。空格处要填的是对某事物造成的伤害。damage一词表示“伤害时要用介词to连接宾语。例如：The storm did a lot of damage to the crops．暴风雨使庄稼受到了很大损失。
单选题 A. as for B. since C. after D. because of
【正确答案】 C
【答案解析】考查连接词的用法。as for至于；because of因为，由于；since自……以来。
单选题 A. life B. gas C. air D. surroundings
【正确答案】 B
【答案解析】根据下文提到恐龙无法呼吸，可以判断出科学家认为地球上的空气发生了变化，因此答案是air。
单选题 A. so heavy B. too heavy C. heavy enough D. heavy as
【正确答案】 D
【答案解析】考查词组结构too...to...“太……以致不能”，符合文中“恐龙身体太重以至于很难移动”。
单选题 A. for eating B. to have C. to survive D. for life
【正确答案】 C
【答案解析】本句大意是：恐龙找不到足够的食物，无法生存下去。选项C中的survive是“活着，继续存在”的意思。