When the subject is the singular third person, the verb should add es when it ends with s, ES, th, SH, O. does this formula have to be used in the singular third person? If so, how to understand this sentence on the basis of the first two sentences,

When the subject is the singular third person, the verb should add es when it ends with s, ES, th, SH, O. does this formula have to be used in the singular third person? If so, how to understand this sentence on the basis of the first two sentences,

Yes, the verb only uses the third person singular when the subject is the third person singular (he, she, it, Xiaoming, Li Hua, Mr Green, etc.)
1. It's usually a verb with s, such as Li Ming runs everyday.run It's a direct addition of S
2. The verbs ending with s, ES, th, SH, O should add es. for example: Li Ming teachers English

Is a EI o u a vowel?

It's a vowel

Is there a vowel / I in a

In a is [EI]
Diphthong