第三人称单数后的can用不用加s
不用加s,因为can是情态动词,它不随人称的变化而变化,无论是第几人称,或单数或复数,can都不变。
例如 I can go to school
We can go to school 
She can go to school
They can go to school
但是 can 有时态的变化
它的过去式是could,过去否定形式是couldn't.
不用加s,因为can是情态动词,它不随人称的变化而变化,无论是第几人称,或单数或复数,can都不变。
例如 I can go to school
We can go to school 
She can go to school
They can go to school
但是 can 有时态的变化
它的过去式是could,过去否定形式是couldn't.