状语从句
　　状语从句就是充当句子状语的从句，它可分为时间、地点、方式、比较、原因、结果、目的、条件和让步等从句。
　　1. 时间状语从句
　　1)常用来引导时间状语从句的连接词有as, when, whenever, while, before, after, till, until, since, as soon as, hardly / scarcely … when, no sooner … than …等。如：
　　He made a mistake, but then he corrected the situation before it got worse.
　　Jack had scarcely / hardly seen me when he left the room.
　　2) 某些表示时间的副词、名词短语和介词短语也可引导时间状语从句。如directly, immediately, the instant, the moment, the minute, the day, the year, each / every time, next time, the first / second / last time, by the time等，如：
　　Directly I received your letter, I came back at once.
　　2. 地点状语从句
　　地点状语从句一般由where, wherever, everywhere和anywhere引导。如：
　　Wherever he went, he was warmly welcomed.
　　3. 原因状语从句
　　原因状语从句一般由because, as, since, now that, in that, seeing that, considering that, now that … but that, by reason that, for the reason that, on the ground that等引导。如：
　　As it is raining, let’s stay at home.
　　A gas differs from liquid in that it has no definite shape.
　　4. 结果状语从句
　　结果状语从句由so … that, such … that, so that, such that, so, that, to such a degree that, to such an extent that, with the result that等引导。
　　The shock was such that she was almost driven mad.
　　The temperature rose to such an extent that the firemen had to leave the house.
　　注：so和such位于句首时，主句需用倒装语序。如：
　　So fierce was their dog that no one dared come near.
　　5. 目的状语从句
　　目的状语从句常由that, so that, in order that, lest, for fear that, in case等引导。从句谓语常由“can / could, may / might + 动词原形”构成，有时也用“shall / should, will / would + 动词原形”。如：
　　We left early so that we could catch the first train.
　　He ran away lest he (should) be caught.
　　6. 条件状语从句
　　条件状语从句由if, unless, only if(只要), if only(但愿), when(如果), suppose / supposing(假如), as / so long as(只要), given that(假设), provided / providing that(假如), granted / granting (that)(假定), on condition that(条件是……)等引导。如：
　　I’ll lend it to you as long as you handle it with care.
　　注：若主句为一般将来时，条件状语从句中谓语需用一般现在时代替将来时。如：
　　If you are free tomorrow, I will go to see you.
　　但如果从句表示的是主语的意志、志愿或以you作主语表示请求时，则用will, would。如：I’d be very glad if you would come. 如果你肯来我会非常高兴。
　　7. 让步状语从句
　　让步状语从句由as, though, although, even if / though, whatever, whoever, whichever, however, whether … or …, no matter + wh-词, be, while, granted that, for all that等引导。如：
　　While / Although he has some shortcomings, he also has some good points.
　　Be it rain or shine, I must go.
　　注：as和though引导的让步状语从句通常用倒装结构，as必须用倒装结构，though可用也可不用倒装。这种倒装通常是把从句中的表语、状语或谓语动词放在句首。如：
　　Selfish as / though he is, he is not without merits. 尽管他自私，但不是没有优点。
　　8. 方式状语从句
　　方式状语从句由as, as if / though, the way, how, as … as, not so / as … as, just as (… so)等引导。如：
　　It looks as if / as though it is going to rain.
　　Do it the way (that) you were told.