先看这个句子：
Do you mean this is the best one ---------这里,this是从句部分的主语.现在,你对this提问时,问句是：Which do you mean is the best one ---------which is the best one -------由此,我们可以看出,could you tell me which is the best one?是正确的表达.当然,也有人会认为could you tell me which the best one is?是正确的表达,因为在他们看来,the best one做从句的主语.лл������¥����λ��˵������ʲô�������أ�which one���������