【译文】这是个困难而又糟糕的事，因为如果动物出生后不得不从头学习生存本领，并且仅仅依靠尝试错误体验世界，那么只有极少数动物能够存活，因为它们做出的决定有可能是致命的。

　　【析句】复合句。主句由and连接两个并列句子组成，This is a difficult and unpleasant business and few animals would survive, and前的句子是简单句，and后的句子后又跟有if引导的条件状语从句和for引导的原因状语从句for there are decisions,decisions又有which引导的定语从句修饰。

　　17. Vigorous criticism is constructive in science more than in some other areas of human endeavor because in it there are adequate standards of validity which can be agreed upon by competent scientists the world over.(1992. 阅读. 6. Text 3)

　　【译文】激烈的批评在科学界比在其他人类智慧领域更能起到建设性的作用，这是因为在科学世界里有足够多的有效标准，这些标准被全世界的优秀科学家们共同认可。

　　【析句】复合句。主句Vigorous criticism is constructive in science more than in some other areas of human endeavor,句中主要包含了比较级，具体是介词短语的比较级。主句后是原因状语从句because there are adequate standards of validity,定语从句which can be agreed upon by...修饰standards of validity。

　　18. He’s a historian of science at Massachusetts Institute of Technology who has discovered something else these two men-and, indeed, most of the major pioneers in science over the last 400 years-have in common: they were, like Sulloway himself, preceded in birth by at least one other brother or sister. (1992. 阅读. 6. Text 4)

　　【译文】他是麻省理工学院的一名科学历史学家，他发现了这两位科学家——实际上也是过去400年里多数科学界领军人物的共同点：那些人和Sulloway自己一样都至少由一个哥哥或姐姐。

　　【析句】复合句。主句He’s a historian of science at MIT，后面是定语从句who has discovered something else,these two men-...-have in common是省略了关系代词that的定语从句修饰something else,破折号内的内容and most of the major pioneers...作插入语。最后，引号后的句子是something else的具体内容。

　　19. There are several steps that can be taken, of which the chief one is to demand of all the organizations that exist with the declared objectives of safeguarding the interests of animals that they should declare clearly where they stand on violence towards people. (1993. 阅读. 6. Text 1)

　　【译文】可以采取若干措施，其中最主要的是要求所有宣称保护动物权益的组织明确表明他们在暴力袭击事件中所持的立场。

　　【析句】本例句中包含多个层层相扣的从句。主句很简单，There are several steps,steps后紧跟有定语从句that can be taken, of which相当于of several steps,引导非限制性定语从句修饰several steps。而of which the chief one is to demand of all the organizations...that...中，包含短语demand of sb that...,to demand of为不定式作表语，all the organizations作demand of的间接宾语，并且后面有that exist with the declared...animals作定语从句修饰，demand的直接宾语是that宾语从句that they should declare where they stand on...,where引导declare的宾语从句。

　　20. Thus, for those individuals who are interested in preserving both the quality and quantity of life, personal health choices should reflect those behaviors that are associated with a statistical probability of increased vitality and longevity. (1993. 阅读. 6. Text 4)

　　【译文】因此，对于那些有心保持生活数量和质量的人来说，个人的健康选择应该能够反映那些从数据上显示可能使人提高活力、延长寿命的行为。

　　【析句】复合句。句首，for those individuals后有定语从句who are interested in preserving...life修饰those individuals,句中是主句personal health choices should reflect those behaviors,而behaviors后也有that引导的定语从句修饰。主句前后都有从句修饰，句子结构是对成的。

　　21. A research paper, assigned in a course and perhaps checked at various stages by an instructor, leads you beyond classroom, beyond the texts for classes and into a process where the joy of discovery and learning can come to you many times. (1994. 阅读. 1. Text 3)

　　【译文】导师在某门课程上布置研究论文，并在不同阶段进行检查，这能够使你的学习超越课堂，超越课本，进入到一个你能多次体会学习和发现的乐趣的过程。

　　【析句】复合句。主句是A research paper leads you beyond...,beyond...and into a process。谓语动词leads后有多个并列的介词短语。而assigned in a course and checked at...instructor是过去分词作定语修饰a research paper,同时也是插入语。最后，在a process后有where引导的定语从句修饰。