阅读理解

Directions: There are 7 passages in this section. Each passage is followed by some questions or unfinished statements. For each of them there are four choices marked A, B, C, and D. You should decide on the best choice. 

Passage 4

For centuries, explorers have risked their lives venturing into the unknown for reasons that were to varying degrees economic and nationalistic. Columbus went west to look for better trade routes to the Orient and to promote the greater glory of Spain. Lewis and Clark journeyed into the American wilderness to find out what the U. S. had acquired when it purchased Louisiana, and the Apollo astronauts rocketed to the moon in a dramatic show of technological muscle during the cold war. 

Although their missions blended commercial and political- military imperatives, the explorers involved all accomplished some significant science simply by going where no scientists had gone before.

 Today Mars loomsas humanity’ s next great terra incognita. And with doubtful prospects for a short-term financial return, with the cold war a rapidly fading memory and amid a growing emphasis on international cooperation in large space ventures, it is clear that imperatives other than profits or nationalism will have to compel human beings to leave their tracks on the planet’ s reddish surface. Could it be that science, which has long played a minor role in exploration, is at last destined to take a leading role? The question naturally invites a couple of others: Are there experiments that only humans could do on Mars? Could those experiments provide insights profound enough to justify the expense of sending people across interplanetary space? 

With Mars the scientific stakes are arguably higher than they have ever been. The issue of whether life ever existed on the planet, and whether it persists to this day, has been highlighted by mounting evidence that the Red Planet once had abundant stable, liquid water and by the continuing controversy over suggestions that bacterial fossils rode to Earth on a meteoritefrom valuable data about the range of conditions under which a planet can generate the complex chemistry that leads to life. If it could be established that life arose independently on Mars and Earth, the finding would provide the first concrete clues in one of the deepest mysteries in all of science: the prevalence of life in the universe. 

单选题 According to the passage, the chief purpose of explorers in going to unknown places in the past was________.
【正确答案】 D
【答案解析】第一段第一句说到探险家不断探索未知领域的原因是“to varying degrees economic and nationalistic” , 即为了追求经济效益, 显示国家实力。
单选题 At present, a probable inducement for countries to initiate large-scale space ventures is ________.
【正确答案】 B
【答案解析】第三段中说到“imperatives other than profits or nationalism” 将会促使人们探索火星, 后面又说道“Could it be that science. . . ” , 也就是说, 促使人们探索火星的一个可能原因是科学研究。
单选题 What is the main goal of sending human missions to Mars?
【正确答案】 A
【答案解析】根据第4段“The issue of whether life ever existed on the planet, and whether it persists to this day. . . ”,由此推断人们探测火星的目的就是想解开此谜。
单选题 By saying “With Mars the scientific stakes are arguably higher than they have ever been” (Line 1, Para.4) , the author means that ________.
【正确答案】 B
【答案解析】本题考查的实际上是对该句中stake一词的理解。 stake在这里指“赌注, 赌金” 。 由于这一段后文谈论的都是火星探测的重要性, 因此推知这一句的意思是对火星进行科学探索会有很高的回报。
单选题 The passage tells us that proof of life on Mars would________.
【正确答案】 C
【答案解析】文章最后一段说到“A more conclusive answer about life on Mars, past or present. . . that leads to life” , 也就是说, 如果在火星上发现了生命, 将给科学中最深奥秘之一的“宇宙中生命普遍存在” 问题提供第一个具体线索, 即将会揭示生命起源的条件。