Question

I remainded in the office until 5:30 ___all the others had left.

I remainded in the office until 5:30 ___all the others had left.A.at which B.when C.which D.that选哪个为什么？

Answer 1

选B,
原因是：首先，后半句应该是定语从句，先行词是5:30 ，在从句中中作时间状语，应该用连接副词when也引导，这时可能你会说when=介词+which,为什么不选A
原因是：从句中时态用had left，也就是过去完成时，如果句子用过去完成时，那么时间状语应该是 by+ which= when

Answer 2

B
___all the others had left是时间状语从句

Answer 3

B
时间状语从句，A应改为on which

Answer 4

D！~