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
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
B
选B。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’。