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【单选题】

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 by going where no scientists had gone before. Today Mars looms (隐约出现) 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 suce. 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 human could do on Mars7 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 the bacterial fossils rode to Earth on a meteorite (陨石) from Mars. A more 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. What is the main goal of sending human missions to Mars

A.
To find out if life ever existed there.
B.
To see if humans could survive there.
C.
To prove the feasibility of large-scale space ventures.
D.
To show the leading role of science in space exploration.
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A.
双层导管结构
B.
牙源性上皮岛
C.
角化珠
D.
角质栓塞
E.
胶样小体

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A.
房性期前收缩
B.
交界性期前收缩
C.
室性期前收缩
D.
交界性逸搏
E.
预激综合征

【单选题】软件工程的出现是由于()。

A.
程序设计方法的影响
B.
软件产业化的需要
C.
软件危机的出现
D.
计算机技术的发展

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A.
缺铁性贫血
B.
溶血危象
C.
红血病
D.
白血病前期
E.
恶性贫血

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A.
转移症状
B.
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C.
上腹痛及脊背痛
D.
消化道症状
E.
贫血、消瘦

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A.
生理、心理和社会环境的因素
B.
个人、集体与社会的因素
C.
感情与理智的冲突
D.
坦率与封闭的矛盾

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A.
紫雪丹
B.
安宫牛黄丸
C.
牛黄清心丸
D.
牛黄上清丸
E.
牛黄解毒丸