“Then what you're saying, Dr. Applebaum, is that it isn't the violence on TV but the unreality that is doing harm to children.”

that it isn't……：是表语从句，用it isn’t引出强调的部分the violence和the unreality。如果不用强调的手段，这个表语从句应为that the unreality, not the violence is doing harm to children.那么原句中的but the unreality that里that是定从引导词吗？