21．Inability to build high-voltage generators and motors gives to the transformer immediate  recognition as a highly flexible link between the generation and distribution of electrical energy．
　　制造高压发电机和高压电动机是不可能的，这就立即使人们认识到变压器是发电与配电之 间灵活性很高的中间环节。  (本句是简单句。主语是inability，谓语是gives，宾语是recognition。不定式短语to build。．．motors作定语，修饰inability。give recognition to．．．as．．·，“承认……是……”。介词短语between—．energy作定语，修饰link。)
来源：考试大
　　22．The mildness of its climate，with slight temperature variations and infrequent rainfall，combined with a high average level of sunshine and brilliant shies，a11 make it idea for tourism  whether by winter or by summer．   
　　宜人的气候、变化不大的温度、稀少的雨量、灿烂的阳光以及明媚的天空，所有这一切使 突尼斯成为冬夏理想的旅游胜地。(with．．．和combined with把三个主语连接起来。all是总括词，总括上述的三个主语。idea是it宾语补足语。it代替上文中Tunisia突尼斯。bywinter．．．这里by作“当……时候”解。例：They don't work by day but by night．他们日间不工作，夜间工作。whether．．or，“不论是……还是”，用作连词，连接两个并列成分。)
来源：考试大
　　23．We explain the differences between gases and liquids bysaying that the molecules in a liquid are not moving about so fredy as the molecules in a gas and are very much closer together．
　　液体分子不像气体分子那样能自由地到处运动，而是比较紧密地聚集在一起，我们以此来解释气体和液体之间的区别。(介词短语by saying．．．作方式方法状语，说明谓语explain。)
来源：考试大
　　24．For about the last 200 years，the structural theory has been devdoped by scientists，mathematicians and engineers，with the very practical object of providing a reliable basis for the design of structures by calculation．
　　大约近200年来，科学家、数学家和工程师们发展了结构理论，其目的在于通过计算给结构物的设计工作提供可*的基础。  (with．．．obiect．．．for．．．是介词复合结构，起目的状语作用。)
来源：考试大
　　25．By the quiet persistence of the truth-seekers，  working upstream against the flow of ancient prejudice，mankind has entered into new realm of health，and the borderlines of death have been  pressed farther back．
    由于真理探索者顶着守旧派偏见的逆流，默默无闻、坚持不懈地努力工作，人类才得以进 入了新的健康王国，而死亡的界线则被抛到离我们更远的地方。(介词短语By．．．truth-seekers用作原因状语，说明谓语动词hasentered。)   
来源：考试大
　　26．When a man picks up a weight from the floor and raises it above his head，  he has in effect  inserted his body between the weight and the earth and pushed the weight one way with his hands，and thee arth the other way with his feet．
　　当一个人从地板上拿起重物并把它举到头顶上时，实际上他是把自己的身体置于重物与地 面之间，他用双手朝着一个方向推着重物，而用双脚朝着另一方向推着地面。(pick up，“拿起”。in effect，“实际上”。one way，“朝着一个方向”。the other way，"朝着另一方向”。这两个短语前均省略介词in，作状语。and与the earth之间省略了谓语pushed。)

　　27．But this is not possible because of the size of the country，with the distance from Dehli to Madras，for example，being greater than that from London to Rome．
　　但这是不可能的，因为印度面积大，譬如，从德里到马德拉斯的距离，就比伦敦到罗马还 要远。(with，名词+分词的结构，可用作状语和定语。句中with the distance．．。being用作定 语，对size进行补充说明。that from．．．that代替distance。)
来源：考试大
　　28．Even at this moment many Of the earth's natural treasures are being destroyed，manyvaluable animals and plants are been killed off，it is becoming increasingly difficult to grow enough  foods to preserve much of the earth's population from stavation．
　　甚至现在，地球上的许多自然财富正遭到破坏，许多珍稀动植物已面临灭绝之灾，为使地球上大多数人口免于饥饿而生产出足够的粮食也越来越困难了。(to preserve．．．from，“使……免于”。)
来源：考试大
　　29．If the Earth，Moon and Sun move into a direct line，with the Moon in the middle，the dark body of the Moon blots out the briliant disk of the Sun，and we witness a solar eslipse．
　　假如地球、月球和太阳运行到一条直线上，月球在中间，那么月球的暗体就遮住了太阳的亮盘，于是我们便看到日食。(with the Moon in the middle是with引出的介词复合结构，在句中起补充说明作用。)
来源：考试大
　　30．As natural science treats of the mutual transformation，changes and development of various kinds of matter，it is of great tmportance for us to make a profound study of it so that we may control the phenomena of nature．  
自于自然科学研究的是各种物质的相互转化、变化和发展，因而我们深入研究自然科学以便控制各种自然现象，这具有重大意义。(treat of．．，"论述”。带逻辑主体for us的不定式短浯to make．．．nature作主语，it是形式主语。so that引导目的状语从句。be of．．，“具有”。)