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：

01

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)

02

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.

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