条件从句
　　由 if, unless, as (so) long as, provided / providing (that), suppose / supposing (that), in case 　　等引导，如：
　　　　If he comes I'll tell you.
　　　　You would have succeeded if you had tried harder.
　　　　You will fail unless you work hard. (=You will fail if you don't work hard.)
　　　　Supposing / Suppose it rains, shall we have the match as scheduled?
　　　　In case you need anything else, please let me know.

　　让步从句
　　由 although, though, even though, even if, whether ... or, while, as, wh-words + ever (= no matter + wh-words) 　　　等从属连词引导，如：
　　　　He is quite modest though he is the best student in the class.
　　　　The needle has the same mass whether it is hot or cold.
　　　　Whichever(No matter which) plan you adopt, you will meet with difficulties.

　　使用上述让步从句的某些从属连词时注意以下几点：
　　　　a.although (though) 不可与连词 but 连用；
　　　　b.as 引导的从句意义和 though 相似，但表示的语气较强，并须将强调的词放在句首（但不用 although），如：
　　　　　Simple as(though) the question may seem, it is not at all common in nature.
　　　　c.however / no matter how 引导的从句中，however / no matter how 后须紧跟形容词或副词，如：
　　　　　However / No matter how hard I tried, I couldn't remember all the questions.

　　对比从句
　　表示两个人或两件事之间的对比，常用 while 或 whereas 引导，如：
　　He is idle, while his brother is diligent.
　　Some people like fat meat, whereas others hate it.