英语翻译为什么是where did you buy this?而不是where you buy this?为什么要加DID还有你昨天干吗?为什么有是what were you doing 为什么又要用WERE搞不懂啊

did是助动词，没有did那句子不通。因为是过去买的，所以是where did you buy this.
what were you doing?你那时在干吗？
what are you doing?你现在在干吗？
别纠结了，学累了你就歇会，这都固定搭配，没啥好吵的。。

特殊疑问句的构成是特殊疑问词（如what,who）+一般疑问句所以第一句where did you buy this?中有DID第二句,因为是问你昨天在干什么,所以肯定是过去式 are的过去式were 至于什么时候用do,什么时候用be,要看后面的动词...