--It’s a pity that you didn’t come to my birthday party last night.--I’m terribly sorry. I

问题补充：

--It’s a pity that you didn’t come 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

答案：

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。