Unluckily his parents were out of work ____he dropped out of school

题目

Unluckily his parents were out of work ____he dropped out of school
A.after that B,after which C after whom Dafter them

答案

B
after 介词在定语从句关系词前面的话,关系词不能用that,用which,which指代的是前面这一件事（他父母不幸失业这件事）,在定语从句中作介词after的宾语
whom是指代人的,不是指代事的,不能选C
after them成为两个句子,两个句子要么用并列句形式要么用复合句,不能这么连接的,因此D也不对