同学你好，该知识点来自沪江网校《英语零基础直达CET6级考试版》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，你好！
can情态动词，不需要根据主语变化。do和be动词需要根据主语变化。其实不管是否是省略，正常句子里就是这样使用的。例如：
1. I   can speak English.      He can speak English.  （can跟着不同主语后面保持原形不变）
 -Can he speak English?   -Yes,he can./No,he can't.
2. - Do you like apples?     -Yes,I do./No,I don't.
   - Does he like apples?   -Yes,he does./No,he doesn't.（he是单数第三人称，do变成does。问句和答句都用的does）
3. They are playing football now.     He is playing football now.（he是单数第三人称，are变成 is）
- Are they playing football now?   -Yes,they are./No,they aren't.
-Is he playing football now？    - Yes,he is./No,he isn't.

如果还有疑问，欢迎同学追问，祝同学学习进步~~