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 science simply by going where no scientists had gone before.

　　Today Mars looms as humanity's next great terra incognita(未探明之地).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 in vites a couple of others:Are there experiments that only human could do on Mars?Couldthose 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 thatthe Red Planet once had abundant stable,liquid water and by the continuing controversy over suggestions the bacterial fossils rode to Earth on a meteorite(陨石)from Mars.A mor conclusive answer about life on Mars,past or present,would give researchers invaluable 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.

　　1.For What purposes did the explorers go the unknown places in the past?

　　2.In the exploration of Mars,_______________________still remains uncertain.

　　3.What has long been regarded as unimportant in the past explorations?

　　4.What has been found on a meteorite from Mars?

　　5.The conditions under which life originates would be revealed with the proof of_________________on Mars.

　　答案：

　　1.[For economic and nationalistic purposes.]

　　[定位]根据explorers go to unknown查找到全文首句。

　　解析：首句中提到，几个世纪以来，出于或多或少的经济原因及国家主义原因，探险家冒着生命危险深人到未知领域。本题是询问原因，所以reasons的定语从句中的内容即为答案For economic and nationalistic purposes。

　　2.[the prospects for a short-term financial return]

　　[定位]根据Mars，uncertain查找到第3段前两句。

　　解析：第3段第2句提到，探索火星在短期内未必能有经济回报。题干中的uncertain对应原文中的doubtful，因此本题答案为the prospects for a short-term tinancial return。

　　3.[Science.]

　　[定位]根据has long和exploration查找到第3段第3句。

　　解析：原文该句提到，在以往探险中一直扮演次要角色的科学这一次终于注定是主角了吗?说明在以往探险中，一直被认为不重要的就是科学，题干中的unimportant对应原文中的a minor role，所以答案为Science.

　　4.[Bacterial fossils.]

　　[定位]根据on a meteorite from Mars查找到末段第2句。

　　解析：末段第2句中suggestions后的内容表明从火星落到地球上的陨石里含有细菌化石，所以本题答案为Bacterial fossils.

　　5.[life]

　　[定位]根据conditions under which查找到末段倒数第2句。

　　解析：原文结构比较复杂，分析其句子结构后可知，火星上生命存程的证据可使研究者了解在何种条件下生命会出现，也就是说，在何种条件下生命会出现可以通过火星上生命存在的证据显示出来。因此答案为life。

（实习编辑：王晓晓）