2.状语从句：此处所说的状语从句用法仅包括条件(if和unless引导)状语从句和时间(when等引导，见下文)状语从句。状语从句需注意以下问题：

1主句若是一般将来时、祈使句或含不表过去的情态动词等，则if(如果)， unless(除非)，when(当…的时候)， as soon as(一…就…)，before, after, until, till, as(当…的时候)所引导的状语从句用一般现在时。

You may take a rest when you finish doing your work. (主句有情态动词)

Could you look after my son after I leave home?

(情态动词could是为了让语气委婉，并不指过去时，从句仍用一般现在时)

I will go out as soon as it stops raining this afternoon. (主句是将来时)

Wait for your brother at the bus station until he arrives. (主句是祈使句)

2而主句若是一般过去时，从句也要用表过去时的适当时态，如：

I would give the money to the charity if I had a million dollars。

When he got to the park, his classmates had left。

My son ran towards me as soon as he saw me on the street。

3.定语从句：定语从句是指修饰前面名词或代词的句子。从句前面的名词或代词叫先行词，从句中的引导词叫关系代词或关系副词。关系代词who只指人，which只指物。that既可指人又可指物。whose 后必须跟有名词，既指人，也可指物。关系词作主语时，不可省略，作宾语时可省略。whom只指人，只作宾语。关系副词where指“在那里”，when指“在那时”。 (以下所给例子凡斜体字部分均作定语从句。)

She is a girl who / that is beautiful and kind-hearted. The girl who / that is tall is my sister。

(以上关系词作主语，不可省略。)

She is a girl (who / whom / that) I know very well. (关系词做know的宾语，可以省略。)

That boy whose hair is very long is my brother. I own a bike whose price is high。

(关系词whose表所属，后需接名词。前句指人，译为“这个孩子的”;后句指物，译为“这个自行车的”。)

I bought a watch (which / that) I paid 100 yuan for. (指物， 作pay的宾语，可以省略。)

I prefer a place which / that is clean and quiet. (关系词译为“这个地方”，主语，不可省)

I prefer a place where I can live a quiet life. (关系词译为“在这个地方”，是地点副词。)

I shall never forget the day when a boy helped me find my dog. (“在这一天”，是时间副词)