--It’s a pity that you didn’t e to my birthday party last night.
--I’m terribly sorry. I for an important lecture.
A. prepared
B. was preparing
C. had prepared
D. has prepared
网友回答
A. prepared
(答案→)B. was preparing
C. had prepared
D. has prepared
解析：句意:——可惜你没来参加我的生日聚会昨晚。——我很抱歉。我当时正在为一个重要的讲座做准备。prepare准备......；prepare for为......做准备。根据句意昨天晚上没来参加我的生日聚会，所以应是当时正在为一个重要的讲座做准备，因此用过去进行时，故选B。