He came back late which time all the guesses had already left.A. byB. atC. duringD. aft

问题补充：

He came back late, which time all the guesses had already left.

A. by

B. at

C. during

D. after

答案：

(答案→)A. by

B. at

C. during

D. after

解析：介词辨析.在表示时间时,by在……之前；at表示在具体时刻；during表示在……期间；after表示在……之后。句意：他回来晚了，在那之前客人们已经离开了。选A。