(2013·吉林四校高三一诊)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
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(答案→)A. couldn't have found
B. mustn't have found
C. couldn't find
D. wouldn't find
解析：A 句意：我真的不知道该怎样感谢你，没有你的帮助，我不可能找到我丢失的项链。couldn't have done表示对过去情况的否定推测，意为“不可能”。