作用二：助動do

　　do作助動詞時，只有do, does, did三種形式，無詞義，限用于含行為動詞的一般現(xiàn)在時和一般過去時兩種時態(tài)的否定句和疑問句中。如：

　　①They don't have any tickets for tonight's concert.

　�、贙ate stayed at home last night, didn't she?

　　③How many books does the library have?

　�、躍he doesn't do the washing in the evening.

　　作用三：替代do

　　為避免動詞的重復(fù)，使語言簡練，常以do, does, did替代前文所用的行為動詞。如：

　�、賂om runs much faster than you do.

　　②-Lucy, can you get some more tea, please?

　　-Sure. I'll do it right away.

　　②-Who broke the cup?

　　-Mimi did.

　�、�-I like bananas.

　　-So does he.

　　作用四：語氣do

　　為突出感情色彩，do常用于祈使句、強調(diào)句和倒裝句中，以加強語氣。如：

　�、貲o be careful.

　　②Don't tell a lie.

　�、跦e did come.

　　④-You often go to the park.

　　-So we do.