⑤译成目的分句。
This body of knowledge is customarily divided for convenience of study into the classifications: mechanics, heat, light, electricity and sound..为了便于研究起见，通常将这门学科分为力学、热学、光学、电学和声学。 (4)不译：不译或省略翻译是在确切表达原文内容的前提下使译文简练，合乎汉语规范，决不是任意省略某些介词。
①表示时间或地点的英语介词，译成汉语如出现在句首，大都不译。如：
There are four seasons in a year. 一年有四季。
Many water power stations have been built in the country.我国已建成许多水电站。
②有些介词如for(为了)，from(从……)，to(对……)，on(在……时)等，可以不译。如：
The barometer is a good instrument for measuring air pressure.气压计是测量气压的好仪器。
The air was removed from between the two pipes.两根管子之间的空气已经抽出。
Answers to questions 2 and 3 may be obtained in the laboratory.问题2和3的答案可以在实验室里得到。
Most substances expand on heating and contract on cooling.
大多数物质热胀冷缩。
③表示与主语有关的某一方面、范围或内容的介词有时不译，可把介词的宾语译成汉语主语。如：
Something has gone wrong with the engine.这台发动机出了毛病。
Gold is similar in color to brass金子的颜色和黄铜相似。
Its never occurred to me that bats are really guided by their ears.我从未想到蝙蝠居然是靠耳朵引路的。
④不少of介词短语在句中作定语。其中of(……的)往往不译。如：
The change of electrical energy into mechanical energy is done in motors.电能变为机械能是通过电动机实现的。 (of短语和change在逻辑上有主谓关系，可译成立谓结构。)
Some of the properties of cathode rays listed below.现将阴极射线的一些特性开列如下。(第一个of短语和some在逻辑上有部分关系，Of不译出。)