Who clean the blackboard yesterday?
问题描述:
Who clean the blackboard yesterday?
答案是John did.就是想问问为什么是did而不是cleaned?
问题打错了是who cleaned
答
john did did就代指(cleaned the blackboard)
如果说john cleaned 就缺少一个宾语 如果说John cleaned the blackboard 又显得没John did那么简洁 所以就不说john cleaned