—Mary do you still remember the first time we met?—of course You Helen’s birthday party

问题补充：

—Mary, do you still remember the first time we met?

—of course, You Helen’s birthday party with your friends in a restaurant.

A. attended

B. had attended

C. were attending

D. have attended

答案：

A. attended

B. had attended

(答案→)C. were attending

D. have attended

解析：这里表示“你当时和你的朋友们正在饭店里参加Helen的生日聚会。”表示过去某一时间正在进行的动作，用过去进行时，故选C。