概念：当宾语从句主句中 主 谓是I think, I BFLIEVE，I'M SURE 等等表示第一人称推测与想法的搭配时，反义疑问句主语和谓语要和原句中从句主语和谓语相同。不过这个句子在主句与从句都用了否定，由于关系到否定转移，这个情况一般被视为错句。而且know 在这类句式中也少见。不过题目中的句子可改为：I don't know if she can play the piano,can she？这样就通顺多了。再讲讲用法，比如I think he is a good man,isn't he? 这里反义问句主谓都与从句（he is a good man）一致，而与主句I think无关。类似的还有I believe that we c
can she?宾语从句，反义疑问句应询问从句主语，就是这样。Good luck! 例子有很多啊I don't think he will come, will he?I can't believe she did so well, did she?再来个肯定的I'm sure he is her father,
