66.You should also learn as much about chemistry as possible from your own experience in the laboramry and from your observations of chemical substances and chemical reactions in everyday life．

　你们也应该从你们自己的实验室经验中，从你们日常对化学物质和化学反应的观察中学习更多的化学方面的知识(1earn．．．from．．，　“从……学……”。句中两个from均为learn要求的。)

　67．You will notice that specific gravity is always the ratio of two weights，and so it is a pure number，such as 3 or 5．25，with out any unit associated with it．

　你们将注意到，比重总是两个重量之比，因而它是一个纯数，譬如3或5．25，无需给它。

定义任何单位。(without．．it是分词复合结构，有结果的意味。)

　68．With the increased productionmade possible by the assembly line，automobiles became much cheaper，and more and more people were able to offord them．

　由于装配线所带来的增产，汽车价格便宜多了，买得起汽车的人越来越多。　(介词短语with…用作原因状语。)

69．Today physicists find that light has the characteristics of both waves and particles with one aspect sometimes predominating and sometimes the other．

　物理学家现在发现，光具有波粒二重性，有时波动性起主要作用，有时粒子性起主要作用。(with。．．the other是分词复合结构，在句中作补充说明。)

70．It is amatter of common observation that a body A cannot exert force on a second body B without B at the same time exerting force on A．

　这是我们通常都能观察到的情况：如果物体B没有同时对物体A施加作用力，那么物体A也不能对B施加作用力。　(without引导的介词复合结构为条件状语，用来说明谓语cannot exert。)

　71．Without the sun's light warming the earth's surface，it would be so terribly cold that life　could not exist．

如果没有阳光来加热地球的表面，地球就会变得非常寒冷，使得生命无法生存。(without引导的复合结构，在句中起条件状语作用。)

72．Just as the length and cross-section of the pipe affect the flow of water so it is with conductors of electric current．

正如管道的长度和截面会影响水流一样，导体对电流的影响也是如此。(with表示关系和范围，有“关于”，“对”，“就”之意。)

73．Water vapor may vary from almost nothing to as much as 4％ and is not usually included　with the other constituents which，in terms of global averages，do not vary significantly．

　(大气中)水蒸气的含量是变化的，从近乎为零到多达4％，通常不与其他成分一起计算，根据总平均值来看，其他成分的含量变化不大。(句中with表示事物之间的关系。参看上句。)

74．This atom，with 92 electrons spinning about the closely packed and complex nucleus，is the element uranium，which seems to be the most complicated of the natural atoms．

这一有着92个电子围着又密集又复杂的原子核旋转的原子，就是元素铀。它似乎是天然原子中最复杂的原子了。(句中with引出的是一个介词复合结构，作定语，修饰atoms。)