"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 请教高手

"what was the wrong?""what was the matter?""what was trouble?''what happened?'的区别？？？ what's meaning with " That was then ". 请问下面是什么意思“What was the front door like before the salesman came?" "It was locked." what was he doing? What was he drawing______ what was the date? What was Linguistics? "I asked him what he was doing" 这句话的句子结构怎么分析？“what he was doing"在这是什么成分？ what was the industrial revolution ? what was otherwise 怎么解释？？