i don't know the reason____ jim came so late a why b for why

问题描述:

i don't know the reason____ jim came so late a why b for why

选A,reason后面的定语从句用why或for which引导,why=for which.
b for why错误,如果why改为which就对了。

I don't know the reason____ jim came so late .
a why b for why
x选项是a.