could (不能用 can) have done 表示“过去本能够做某事却未做.”注意:其否定形式 couldn't have done 没有虚拟语气的用法,couldn't have done 只能表推测,相当于 can't have done,意为:“过去不可能做了某事.” 举例:I think that he couldn’t/can't have gone abroad.I saw him just now. 我认为他不可能出国了.我刚才还看见他了. 希望对您有所帮助,如有不懂可再问,如有帮助记得给分哦,!