Be a good boy!

　　Don't be silly!

　　Don't be a fool!

　　Do be obedient!

　　Do be careful.

　　二、be 动词做助动词

　　助动词be 有两个基本用法，一是与谓语动词一起构成各种时态，二是构成被动语态。

　　1、“be + 现在分词组”成各种进行式时态。例如：

　　Tony's maid is washing his new car.

　　The children are playing in the field.

　　Samuel was eating when I came in.

　　We have been living here since 1959.

　　This time next day they will be sitting in the cinema.

　　三、注意事项

　　英语句子中，为了表达时态或被动语态的需要，常常会出现几个助动词连在一块儿使用。也就是说，助动词be会和其它助动词一起使用。这时候，整个句子的一般疑问句和否定句，就不一定是对be 进行变化了，而是以第一个助动词为主进行变化。即哪个助动词在先，就以它为主进行变化。例如：

　　[肯定句] All the wonderful birds can be found in our Bird Park. (助动词有两个：can be )

　　[疑问句] Can all the wonderful birds be found in our Bird Park? (移第一个can)

　　[否定句] All the wonderful birds can not be found in our Bird Park. (在第一个can 后加not)

　　[肯定句] I have been there before. (两个助动词：have, been )

　　[疑问句] Have you been there before?

　　[否定句] I have not been there before.