题目内容：

This is the reason ——I came here
A.that B.why 为什么不用that

优质解答

这句话可以拆分为：This is the reason.I came here for this reason.
合并起来：This the reason why I came here.
如果用that的话,是用来直接和reason同位语.
比如 This is the reason that I give to you.