问题补充:
-Where did you go the morning of April 6?
-I didn’t come to the office the meeting was over.
A. in, when
B. at, unless
C. on, until
D. to, though
答案:
A. in, when
B. at, unless
(答案→)C. on, until
D. to, though
解析:确指某天的上午、下午或晚上时要用介词on not…until固定结构。