单选题 When imaginative men turn their eyes towards space and wonder whether life exists in any part of it, they may cheer themselves by remembering that life need not resemble closely the life that exists on Earth. Mars looks like the only planet where life like ours could exist, and even this is doubtful. But there may be other kinds of life based on other kinds of chemistry, and they may multiply on Venus or Jupiter. At least we cannot prove at present that they do not.
Even more interesting is the possibility that life on other planets may be in a more advanced state of evolution. Present-day man is in a peculiar and probably temporary stage. His individual units retain a strong sense of personality. They are, in fact, still capable under favorable circumstances of leading individual lives. But man"s societies are already sufficiently developed to have enormously more power than the individuals have.
It is not likely that this transitional situation will continue very long on the evolutionary time scale. Fifty thousand years from now man"s societies may have become so close-knit that the individuals retain no sense of separate personality. Then little distinction will remain between the organic parts of the multiple organisms and the inorganic parts (machines) that have been constructed by it. A million years further on man and his machines may have merged as closely as the muscles of the human body and the nerve cells that set them in motion.
The exploration of space should be prepared for such a situation. If they arrive on a foreign planet that has reached an advanced stage (and this is by no means impossible), they may find it being inhabited by a single large organism composed of many closely cooperating units.
The units may be "secondary" —machines created millions of years ago by a previous form of life and given the will and ability to survive and reproduce. They may be built entirely of metals and other durable materials. If this is the case, they may be much more tolerant of their environment, multiplying under conditions that would destroy immediately any organism made of carbon compounds and dependent on the familiar carbon cycle.
Such creatures might be relics of a past age, many millions of years ago, when their planet was favorable to the origin of life, or they might be immigrants from a favored planet.

单选题 Humans on Earth today are characterized by ______

单选题 According to this passage, some people believe that eventually ______

【正确答案】 D

【答案解析】[解析] 第三段指出，50000年以后，人类社会可能会变得如此严格一致，以至于个体不再有独立的个性感。到那时，众多物种的有机部分与社会创造的无机部分(指机器)之间将不再有什么区别。再过100万年，人和他创造的机器会融为一体，正像人体肌肉与使肌肉活动的神经细胞一样密不可分。
第五段指出，这些“单位”可能是“次一级的”(即：不是像人和其他生灵一样是自然中原来就存在的)——它们是以前存在着的一种生命在几百万年前创造出来的机器，并被赋予了生存和繁衍的意志和能力。它们也许是由金属或其他耐久材料制成的。如果是这样，它们对环境的耐力要强得多，在特殊的环境下不断繁衍。这种环境可能会立刻毁掉由碳水化合物构成并依靠为人熟知的碳循环来维系生命的生物。
最后一段指出，这种生物或许是几百万年前的某个时代的遗存物，那时，他们的星球还有利于生命的诞生，又或许是从某个其他适合生命居住的星球上迁移过去的“移民”。
D中的living应理解为与Organic同义。

单选题 Even most imaginative people have to admit that ______

【正确答案】 B

【答案解析】[解析] 第一段指出，当富有想象力的人遥望太空，冥想其他星球上是否存在生命的时候，如果他们记住一点——那里的生命没有必要像地球上的生命一模一样，他们就不会悲观(即：他们就会相信也许有其他生命存在)。火星似乎是我们这样的生命能够存在的唯一星球，但是，即使这种说法也是值得怀疑的。然而，也许有其他种类的有机生命存在，他们也许在金星和木星上繁衍，至少我们目前无法证明他们没在那些星球上繁衍(do not应理解为do not multiply on Venus and Jupiter)。