as, though引导的倒装句
　　as / though引导的让步从句必须将表语或状语提前 （形容词, 副词, 分词, 实义动词提前）。
注意：
　　1) 句首名词不能带任何冠词。
　　2) 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.
注意:
　　让步状语从句中，有though，although时，后面的主句不能有but，但是 though 和yet可连用。

表示一…就…的结构
　　hardly/scarcely…when/before, no sooner…than　和as soon as都可以表示"一…就…"的意思，例：
　I had hardly / scarcely got home when it began to rain.
　I had no sooner got home than it began to rain.
　As soon as I got home, it began to rain.
　注意：如果hardly, scarcely 或no sooner置于句首，句子必须用倒装结构：
　Hardly / Scarcely had I got home when it began to rain.
　No sooner had I got home than it began to rain.

比较and和or
　　1) 并列结构中，or通常用于否定句，and用于肯定句。
　2) 但有时and 也可用于否定句。请注意其不同特点：
　　 There is no air or water in the moon.
　　 There is no air and no water on the moon.
　在否定中并列结构用or 连接，但含有两个否定词的句子实际被看作是肯定结构，因此要用and。
典型例题
　---I don‘t like chicken ___ fish.　
　---I don‘t like chicken, ___ I like fish very much.
　A. and； and　 B. and； but　C. or； but　D. or；and
　答案C。否定句中表并列用or, but 表转折。
判断改错：
　　(错) We will die without air and water.
　　(错) We can‘t live without air or water.
　　(对) We will die without air or water.
　　(对) We can‘t live without air and water.