At home ,he never seems to have time until after 10:30 p.m.,_____his children have gone to bed.

题目

At home ,he never seems to have time until after 10:30 p.m.,_____his children have gone to bed.
A whose time B when C on which D by which time
选什么,为什么?

答案

D（错了表怪偶,好多年不做了）
因为是逗号隔开,而前面一句很显然是一个完整的句子,所以后面会跟一个从句.A很显然不对,连意思都不通；B的话就不要逗号了；C which后面少了time,而且介词貌似也有问题.
所以选D.