同学你好，该知识点来自沪江网校《英语零基础直达PETS四级/公共英语四级【随到随学班】》的课程，想要更系统的学习，欢迎进入课程学习。不仅可以和更多的同学一起学习，而且还有老师、助教随时的学习指导和知识点解答哦。

同学好：
当句意表示“ ... 是 ...（的）”或者“ ... 在某处/某时”，句子里用be 做动词。be 是描述状态的动词。
如：
His brother is a doctor.
We are in Beijing.
Lucy’s birthday is in May.

上述句子中，在变疑问句时，将be 动词提前到主语前面；如：
Is his brother a doctor?
在变否定句时，在be 后面加not；如：
We are not in Beijing.

一般现在时里，当句子的谓语是实义动词，对句子进行提问或者否定时需要用助动词do/does；主语是第三人称单数时用does，其他人称用do。如：
We go to the library on Friday.
一般疑问句：Do you go to the library on Friday?
否定句：We don’t go to the library on Friday.

Peter wants to buy a bike.
一般疑问句：Does Peter want to buy a bike?
否定句：Peter doesn’t want to buy a bike.

请参考以上。

祝学习愉快～