he did not understand English.句中的为什么用did 而不用was?

he did not understand English.句中的为什么用did 而不用was? 英语,【He did not understand English!】主语是单数,为什么不用【understands】? He did not understand English!He spoke German!既然是持续的状态,为什么用过 it did not prove to be a problem为什么用did?不用was I did not enjoy it为什么用did而不用could 比如说She does not understand English.这里面为什么不用She is 而用she does Did he have a key?这里的he是第三人称,为什么不用has而用have? Did not understand your english 翻译一下 谢谢 请问一个英语问题：I did not understand the problem.He explained it 两句 Did he study English when he was four years old?改为肯定句 what did he see when he went into the office?这里为什么用when而不用别的 He did not go to school because he was ill的同意句