Our teacher is always busy preparing lessons until 11 o’clock at night, _______w

题型：不详难度：来源：

Our teacher is always busy preparing lessons
until 11 o’clock at night, _______we students have gone to sleep.

A．that time

B．by which time

C．by that time

D．which time

答案

B

解析

句意为“我们的老师总是忙着备课到晚上11点钟，那时我们已经睡了”。by意为“到……时(为止)”，which time 指代 “11 o’clock at night’。