I you but I was busy all the time yesterday afternoon.A. could helpB. had helpedC. helpe

问题补充：

I you, but I was busy all the time yesterday afternoon.

A. could help

B. had helped

C. helped

D. could have helped

答案：

A. could help

B. had helped

C. helped

(答案→)D. could have helped

解析：英语中，“情态动词 + 完成时”表示“本来……”，讲过去的情况。could have helped：本来能帮助