考博英语词汇 语法题常考知识点专项练习：状语从句
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1.在时间和条件(有时也在方式、让步等)从句中，主句是一般将来时，从句通常用一般现在时表示将来。
e.g. We’ll go outing if it doesn’t rain tomorrow.
I’ll write to you as soon as I get to Shanghai.
2.有些时间、地点、条件、方式或让步从句，如果从句的主语与主句主语一致(或虽不一致，是it)，从句的谓语又包含动词be ，就可省略从句中的“主语 + be”部分。
e.g. When (he was) still a boy of ten, he had to work day and night.
If (you are) asked you may come in.
If (it is) necessary I’ll explain to you again.
3.注意区分不同从句：引导的是什么从句，不仅要根据连词，还要根据句子结构和句意来判别。以where为例，能引导多种从句。
e.g. You are to find it where you left it.(地点状语从句)
Tell me the address where he lives.(定语从句，句中有先行词)
I don’t know where he came from.(宾语从句)
Where he has gone is not known yet.(主语从句)
This place is where they once hid.(表语从句)
1) 时间状语从句
时间状语从句主要由以下连词引导：when, whenever, as, while, since, until, till, before, after, as soon as, once, hardly (scarcely) …when, no sooner …than。
I will discuss the matter with you when we meet tomorrow.
时间状语从句还可由某些可充当连词的名词(the moment, the instant, every time,等)和副词(instantly, directly等)引导：
I will tell you the news the instant I know.
Note:
①before除了可表示“在…之前”外，还可用来强调主句所表达的时间、距离很长或花费的力量相比较大，可译为“…才”。(“not …before”可用来强调主句所表达的时间、距离很短或花费的力量相比较小，可译为“…就”)。
It was a long time before I got to sleep again.
②如果位于when引导的分句之前的主句使用过去进行时、过去完成时或“was/were about to, was/were on the point of”等结构时，when表示突然发生某事，可译为“正在…突然”或“刚…就”等。这时，不能够用as或while来代替when。
I was walking on the street when I ran into my old friend John.
2) 条件状语从句
条件状语从句主要由以下连词引导：if, unless, providing/provided (that), suppose/supposing (that), on condition (that), as/so long as, in case等。
So long as you work hard, you will surely achieve good results in examinations.
3) 让步状语从句
让步状语从句主要由以下连词引导：though, although, even if, even though, whatever, however, whoever, wherever, no matter how/ what/ where/ when等。以下介绍几种较特殊的让步状语从句。
(1)while引导的让步状语从句多放在句首，while相当于although，表示“尽管”，“虽然”。
While I admit I did it, I didn’t intend to.
(2)短语“even now/then/so”相当于“though it is/was true”，表示“尽管如此”，“尽管这样”。
The fire was out, but even so, the smell of smoke was strong.
(3) as引导的让步状语从句要倒装。
Child as he was, he could speak four languages.
4) 比较状语从句
比较状语从句主要由以下连词引导：(not) as …as, (not) the same as, (not) such …as, not so …as, than, the + 比较级…, the +比较级…等。
We have had a lot more rainfall this year than we had last year.