1. while
这个词引导状语从句，但在不同的句中有不同的含义。可以和括号里的词替换。
We must strike while the iron is hot. （as）
While we don’t agree, we continue to be friends. (although)
While I admit his good points, I can see his bad. (although)
Some people waste while others haven’t enough. (but)
While their country has plenty of oil, ours has none. (but)
