问题描述：
he bought a house last year.did he buy a house last year?he did not buy a house last year
1：he bought a house last year.2：did he buy a house last year?3：he did not buy a house last year.为什么第一句用bought,而第二第三句用了buy.第一句用过去式倒还好理解,我就是不能理解第二句第三句为什么用buy与did,因为did是过去式,而buy却没有用过去式,我就是这里搞不明白.
1：he bought a house last year.2：did he buy a house last year?3：he did not buy a house last year.为什么第一句用bought,而第二第三句用了buy.第一句用过去式倒还好理解,我就是不能理解第二句第三句为什么用buy与did,因为did是过去式,而buy却没有用过去式,我就是这里搞不明白.
问题解答：
我来补答展开全文阅读