Single three: refers to the singular third person as the subject, and the predicate verb will change at this time. Now take the simple present tense as an example. Predicate verbs generally add s, or change to the form of single three, such as:

He is a teacher. I am a teacher/we are teachers. )

She works hard. (contrast: you work hard/they work hard)

In other tenses and voices, Dan San has also changed. Pay attention to the explanation of grammar.