—What were you doing at this time yesterday? —I on the grass and playing with Tony. A. si

问题补充：

—What were you doing at this time yesterday?

—I on the grass and playing with Tony.

A. sit

B. sat

C. am sitting

D. was sitting

答案：

A. sit

B. sat

C. am sitting

(答案→)D. was sitting

解析：句意：昨天的这个时间你在做什么?我在草地上坐着和Tony一起玩.过去进行时表示过去某某一时刻或过去一段时间内正在进行的动作.常用的时间状语then,at that time,this time yesterday,at ten yerterday等, 根据语境和题意故选D.