—I knocked into a tree when I went to the bus stop for my friend.—I suppose you too fast.A

问题补充：

—I knocked into a tree when I went to the bus stop for my friend.

—I suppose you too fast.

A. had driven

B. are driving

C. drove

D. were driving

答案：

A. had driven

B. are driving

C. drove

(答案→)D. were driving

解析：句意：当我去公交车站接我的朋友时，我撞到了一棵树上。——我猜你当时开得太快了。结合语境可知下文从句中强调的是过去某时正在进行的动作，故用过去进行时态。选D。