题目内容：

he often does some cleaning on weekends(对on weekends提问)

优质解答

when does he often do some cleaning?

追问：

为什么加do

追答：

因为这是真正的谓语动词啊，前面的does是助动词。在前面你给的陈述句中的does是第三人称谓语动词。不管是改为一般疑问句还是否定句都要借助于助动词does