帮我看看这道定语从句题

题目

帮我看看这道定语从句题
He's bought a cottage in the country for _____he retirees,with the money he's saved he can be half of his life.
A when
B where
C what
D which
选哪个?原因?

答案

D
首先for是介词,后面是不能跟副词的,所以AB是不能选的.
然后定语从句中连接词没有what,所以C也是不能选的.