I really don’t know how to thank you but for your help I my lost necklaceA. couldn’t

问题补充：

I really don’t know how to thank you , but for your help, I my lost necklace．

A. couldn’t have found

B. mustn’t have found

C. couldn’t find

D. wouldn’t find

答案：

(答案→)A. couldn’t have found

B. mustn’t have found

C. couldn’t find

D. wouldn’t find

解析：考查虚拟语气。根据句中but for要不是，用虚拟语气，本题是对过去事实相反的虚拟语气，故用could have done，选A。