— Why didn’t you come to Mike’s birthday party yesterday?　　— Well I but I forgot it.A.

问题补充：

— Why didn’t you come to Mike’s birthday party yesterday?

— Well, I , but I forgot it.

A. should

B. must

C. should have

D. must have

答案：

A. should

B. must

(答案→)C. should have

D. must have

解析：should have的后面省略了come。should have come表示“本应该而实际上没有”。