— Do you know the old man on the bench over there?— He is my grandfather.A. sitB. satC. t

问题补充：

— Do you know the old man on the bench over there?

— He is my grandfather.

A. sit

B. sat

C. to sit

D. sitting

答案：

A. sit

B. sat

C. to sit

(答案→)D. sitting

解析：句意：--你认得那边凳子上的老人吗？--他是我爷爷。这里需要定语修饰the old man，用现在分词做定语，所以选D。