30. —Robert speaking. Could you get me through to Mr. Smith in Room 501?
—I’m sorry, he isn’t here. He ________ this morning.
A. checked in      B. dropped in C. checked out       D. dropped out
30. 【答案】C
【解析】考查动词短语辨析。check in(在旅馆)登记入住, (在机场)检票登机; drop in 顺道拜访; check out 结账退房,结账离开(诊所); drop out 退学;退出(比赛等)。