▲用来替代动词的do是助动词，也可以说用作“代动词”，用来表示刚提到的动作，以避免重复。请看以下例句。
—Do you like Beijing? 你喜欢北京吗？
—Yes, I do. 是的，喜欢。（do用作代动词，代替like Beijing）
I always eat peas with honey. My wife never does. 我总是就着蜂蜜吃豌豆。我的妻子从来不这样吃。（does用作代动词，代替eat peas with honey）
▲但是要注意do so ,do it , do that这种结构，do不是助动词，而是实义动词，而且是及物动词。例如:
She hoped that he would search the room carefully and he did so. 她希望他仔细地检查房间，而他这样做了。
At night, when you really wish to go to sleep, you rarely manage to do so. 夜里当你正想入睡的时候，你却很少能成眠。
I could run after a bus and catch it twenty years ago, but I can’t do that now.
Mr Brown goes to the hospital for treatment every week: in face, he has been doing it ever since I have known him.布朗先生每周去医院治疗：事实上，自从我认识他依赖，他一直就是这样。