都是对的,但后面接的语言材料不同 如：他迟到的原因the reason for his being late=the reason why he wa slate 可见：the reason for 接名词,代词,v-ing形式the reason why 接句子 如不明白请追问,如果满意请【采纳...那如果后边加原因，是用because还是that嗯嗯?The reason for/why.... is that......
之所以。。。。是因为。。。。。
习惯上一般用that