Question

He came back late,___which time all the guests had already left.

A.after B.by C.at D.during

Answer 1

B
首先，从语义上分析，客人们肯定在john回来之前已经离开，之前是by the time
而且，had left是过去完成时，which引导定语从句，which指代john回来那个时候，提示过去时间同时也是过去完成时的标志词组的也是by the time

Answer 2

B.
all guests had already left by that time , 在重句中该成了which

Answer 3

答案选B.by

追问

为什么？

追答

因为后面是过去完成时态

Answer 4

B

Answer 5

C at