．—I did not know you were good friends．
—You ．I have known her since she moved here．You were abroad then．
A. may have
B. needn’t have
C. couldn’t have
D. must have
网友回答
A. may have
B. needn’t have
(答案→)C. couldn’t have
D. must have
解析：考查虚拟语气。句意：我不知道你们是好朋友。——你不可能知道。自从那移居到这儿我就认识他。那时你在国外。“could+have+done”是虚拟语气，表示对过去事情的假设。。故选C。