I could have helped the old man yesterday morning.A. did I comeB. if I cameC. had I comeD

问题补充：

I could have helped the old man yesterday morning.

A. did I come

B. if I came

C. had I come

D. if I should come

答案：

A. did I come

B. if I came

(答案→)C. had I come

D. if I should come

解析：句意:如果我昨天来的话我就能帮助那位老人。这是省略if的条件状语从句，并且是虚拟语气，从句中有过去的时间状语，所以对过去的虚拟谓语应该用had done，省略if时，把had提到主语的前面，故选C。