条件状语从句
可分为真实条件句和if引导的非真实条件句。
I) if, unless 引导的条件状语从句
unless 意义上相当于if…not。 unless一般不用于非真实条件句。重磅阅读
I will not lend the book to you unless you can return it in time.
II) only if和if only引导的条件状语从句
only if意为“只要……”，引导真实条件句，若only if放在句首，后面的主句要用倒装结构。 if only 引导虚拟条件句，也可引导感叹句，意为“但愿……”、“要是……就好了”。
Only if you study hard will you pass the final-examination.
只要你努力学习，就会通过期末考试。
If only we had arrived at the airport in time, we could have met him.
要是我们按时赶到车站，我们也许就能见到他。
If only it would stop raining! 但愿雨能够停下来!
让步状语从句
I) though, although引导的让步状语从句
这两个词同义，但although语气较重，且多用于句首。though引起的状语从句可用也可不用倒装。
Strange though it may seem (Though it may seem strange), he remained single all his life. 他终生未娶，此事似乎令人觉得奇怪。
II) even if 和even though (即使) 引导的让步状语从句
I was persuaded to do the job, even it / even though I didn’t want to.
我被说服去做那件工作，即使我并不想做。
III) as 引导的让步状语从句： 必须用倒装结构——把从句中的表语、状语或谓语动词放在句首。 作表语的名词前如有不定冠词a (an)，再倒装结构中，前面不能再加冠词。
Much as I admired his courage, I don’t think he acted wisely.
尽管我欣赏他的勇气，但我认为他的行为并不明智。
IV)while引导的让步状语从句：意义上相当于although，只能放在句首。
While I understand your viewpoint, I don’t agree with you. 虽然……
V)“whether …or…”, “wh-词+ ever”结构和“no matter + wh-词”引导的让步状语从句，意为“无论……”。 Whatever后接名词，however后接形容词或副词。
Whatever (No matter what) may happen, we will not change our mind.
However often you ring, no one will answer. 无论你打多少次电话，都不会有人接。
All matter, whether it is a gas, a liquid or a solid, expands as the temperature rises.