(1)在reason作先行词的定语从句中,若从句表原因,一般用why引导定语从句,why可以用for which替换.why还可省去.
①The reason why (for which) he has resigned is poor health.他辞职的理由是健康状况不佳.
(2)当reason作主语带有定语从句修饰时,其后的表语从句通常用that不用because.
②The reason why he didn't come in time was that he didn't feel well.
他没有来的原因是因为他不舒服.
(3)当reason用作定语从句的宾语时,引导词用that/which,而且that/which可省去.
③The reason (that/which) he gave for being late was that they were held up in a traffic jam.
他给出的迟到原因是由于他们被交通阻塞给耽误了.
(4)注意句型This/That's why… This/That's the reason why…
④That's why he did it.(不用that代替why)这就是他为什么做这事的原因.
⑤That's the reason why he did it.(口语中可用that代替why)