he didn't go to bed ____ his mother came back last night中间应该填什么?

问题描述:

he didn't go to bed ____ his mother came back last night中间应该填什么?
he didn't go to bed ____ his mother came back last night 中间应该填then until because after 这四个单词中的哪一个?为什么?注意要解释出来为什么填哪个.

until,not .until 直到 .才..