爱华网The reason why he could not go therewas that his grades were too low.
The reason why...is that... 这是特定句型,why引导定语从句,is后的用词为that,一般不用because.
The reason why she did it is that shewouldn’t let her parents feel disappointed.
她为什么做那件事是因为她不想让父母失望。
该句中的why引导一个定语从句，而that引导表语从句。
(1) 句中that引导的表语从句说明主语reason的具体内容
注意以下三种结构：
① The reason is / was that clause.当主语是reason / cause时，一般不能用because或why引导表语从句，以免造成语意重复。
The reason why/for which(也可以省去) he waslate was that he got up late.
他迟到的原因是他起床晚了。
②当主语是This / That时，可以由because /why引导表语从句。
He got up late. That was why he waslate for class.
He was late for class. That was becauseHe got up late.
(2)why在句中是关系副词，引导定语从句，修饰先行词reason，同时它在定语从句中作状语，此时why = forwhich，但要注意：关系词在定语从句中做主语或宾语时，要用关系代词that或which。
The reason why/for which(也可以省去) he waslate was that he got up late.
他迟到的原因是他起床晚了。
The reason that/which/(也可以省去) he gaveyou was reasonable.
他给你的理由是合理的。
【练习】
-- I drove to Zhuhai for the air showlast week.
-- Is that ____ you had a few daysoff?
A.whyB.whenC.whatD. where
变式① Is this the reason ____ at themeeting for his carelessness in his work?
A. heexplainedB. what he explained
C. how heexplained D. why heexplained
变式②The reason ____he failed to pass theexam was ____ he never studied hard.
A. whywhat B.because that C. why that D. why because
变式③Is this the reason _____ he waspunished? Which of the following is wrong?
A.whyB. for whichC.不填D. that
