"Whatwastheteacherlike?""IfonlyIcouldknowher."句子改错答案是把couldknow改成couldhaveknownifonly用过去式或would/could+动词原形表示与现在或未来事实相反的愿望用过去完成式表示与过去事实相

Question

"What was the teacher like?" "If only I could know her."句子改错
答案是把could know 改成 could have known
if only 用过去式或would/could+动词原形表示与现在或未来事实相反的愿望 用过去完成式表示与过去事实相反的愿望 为什么要这样改呀

Answer 1

第一句话决定了时态是过去时,
第二句用了If only虚拟,所以需要在目前的时态的基础上往前再推一个时态,所以把could know 往前推就变成 could have known
表示“我以前认识她就好了”