一、
　　1) 表示目的;它的否定式是so as not to do。
　　Tom kept quiet about the accident so as not to lose his job.
　　汤姆对事故保持沉默是为了不丢掉他的工作。
　　Go in quietly so as not to wake the baby.
　　轻点进去，别惊醒了婴儿。
　　2)　so kind as to ---劳驾
　　Would you be so kind as to tell me the time?
　　劳驾，现在几点了。
　　二、
　　though, although
　　注意： 当有though, although时，后面的从句不能有but，但是 though 和yet可连用
　　Although it‘s raining, they are still working in the field.
　　虽然在下雨，但他们仍在地里干活。
　　He is very old, but he still works very hard.
　　虽然他很老，但仍然努力地工作。
　　Though the sore be healed, yet a scar may remain.
　　伤口虽愈合，但伤疤留下了。 (谚语)
　　典型例题
　　1) ___she is young, she knows quite a lot.
　　A. When　B. However　 C. Although　 D. Unless
　　答案：C。意为虽然她很年轻，却知道许多。
　　2)　as, though 引导的倒装句
　　as / though引导的让步从句必须表语或状语提前(形容词、副词、分词、实义动词提前)。
　　Child as /though he was, he knew what was the right thing to do.
　　= Though he was a small child, he knew what was the right thing to do.
　　注意： a.　句首名词不能带任何冠词。
　　b.　句首是实义动词，其他助动词放在主语后。如果实义动词有宾语和状语，随实义动词一起放在主语之前。
　　Try hard as he will, he never seems able to do the work satisfactorily.
　　= Though he tries hard, he never seems…
　　虽然他尽了努力，但他的工作总做的不尽人意。
　　3)　ever if, even though.　即使
　　We‘ll make a trip even though the weather is bad.
　　4) whether…or-　 不管……都
　　Whether you believe it or not, it is true.
　　5)　"no matter +疑问词" 或"疑问词+后缀ever"
　　No matter what happened, he would not mind.
　　Whatever happened, he would not mind.
　　替换：no matter what = whatever
　　no matter who = whoever
　　no matter when = whenever
　　no matter where = wherever
　　no matter which = whichever
　　no matter how = however
　　注意：no matter 不能引导主语从句和宾语从句。
　　(错)No matter what you say is of no use now.
　　(对)Whatever you say is of no use now.
　　你现在说什么也没用了。(Whatever you say是主语从句)
　　(错)Prisoners have to eat no matter what they‘re given,
　　(对)Prisoners have to eat whatever they‘re given.　囚犯们只能给什么吃什么。