定语从句（1）
一、引导词 1、它的双重作用 (1)在从句中一定有语法成分 (2)一定要代替前面某个词或整个主句，一般它代哪个词从句就修饰那个词(这一点非常重要) Most of the atomic(原子的) mass(质量) is concentrated(集中) in the nucleus(原子核), which explains(解释) why the nucleus is almost(几乎) stationary(静止不动的) within(在…中) the atom(原子).
2、分类 (1)关系代词 that:用于人或物(它一般不能引导非限制性定语从句) which:只能用于事物 who:只能用于人(在从句中作主语) whose:用于人或事物(在从句中作定语，一般译成“其”) as:在科技文中主要用于事物(它有固定的词义“像…那样(的)”) but: ≈ that/which/who …not(目前不作要求) There is another form(形式) of energy(能量), due to(由于) pressure(压力), that we must take into account(考虑).
In this case, that device can produce(产生) a sound(声音) “dit-dah-dit”(滴-嗒-滴) that a radio operator(报务员) who knows the Morse code(摩尔斯电码) will interpret(翻译) as the letter(字母) R. ※There is no material(物质) but will deform(形变) more or less(或多或少) under the action(作用) of forces. 注意：在以下情况，修饰事物的定语从句只能用“that”而不能用“which”来引导。（目前不作要求）
(i)先行词为不定代词时（“something”除外） All that the user(用户) has to do in order to access(存取) the records(记录) is start(启动) a web(网) browser(浏览器) and visit(访问) the web site(网址). Anything that is hot(热的) radiates(辐射) heat(热). (ii)先行词被序数词修饰时 The first component(元件) that will be chosen(选择) in design(设计) is the transistor(晶体管). (iii)先行词被形容词最高级修饰时 Computers are the most efficient(有效的) assistant(助手) that man(人类) has ever(曾经) had.
The best accuracy(精度) that the analog(模拟) computer can achieve(取得) is an accuracy of about(大约) 1 part in 10,000. (iv)先行词被“only/no/very/any”修饰时 The only thing that must be done is (to) measure(测量) the voltage(电压) across the capacitor(电容器).