●Why 指原因，在定语从句中作原因状语。先行词为reason 时，可用for which指代；当关系词在从句中作主语或宾语时，则用which或that 引导。如：

　　The reason why / for which / （that） he didn't attend the meeting was that he was ill.

　　I don't believe the reason （that/which） he gave me. （作宾语）

　　Have you asked him the reason that may explain his success？ （作主语）

　　Ex.） He was late .That's because he got up late.

　　.He got up late. That's why he was late.（表语从句）

　　（the reason） why/for which he was late. （定语从句）

　　当先行词为way时，定语从句常用that， in which，或how引导，that常可以省略。

　　way后的定语从句 的引导词不用时较多。但如果关系词在句中作主语或宾语

　　时，则用which或that 引导。如：

　　This is the way （that） /in which I do such things.

　　比较： Please do the experiment in the way （that/which）I have shown you.