作用二：助動(dòng)do

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

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

　　②Kate stayed at home last night, didn't she?

　　③How many books does the library have?

　　④She doesn't do the washing in the evening.

　　作用三：替代do

　　為避免動(dòng)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(dòng)詞。如：

　　①Tom 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.

　　③-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(qiáng)調(diào)句和倒裝句中，以加強(qiáng)語氣。如：

　　①Do be careful.

　　②Don't tell a lie.

　　③He did come.

　　④-You often go to the park.

　　-So we do.