—You were out when I dropped in at your house.
—Oh,I for a friend from England at the airport.
A. was waiting
B. had waited
C. am waiting
D. have waited
网友回答
(答案→)A. was waiting
B. had waited
C. am waiting
D. have waited
解析：过去进行时可表示过去某一时间正在进行的动作或存在的状态。答语中暗含了when you dropped in at my house。