六级考试阅读理解真题精选练习（20）_大学英语阅读

六级考试阅读理解真题精选练习（20）

　　2014年12月18日我们又将迎来四六级考试，你复习得怎样了?针对大部分考生的备考难点，在线陆续推出四六级词汇、听力和阅读的专项测评以及在线模考，并提供全面综合的复习指导。现在就来参加#四六级测评#吧，每天测评10分钟，轻松搞定四六级，更有每周幸运大抽奖，精彩奖品等你拿!

　　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 Appolo 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 looms as 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?