Subject-verb agreement means that the sentence is grammatically correct. Subject-verb agreement is usually more of a problem in present-tense sentences. Verbs in the past tense don't change as much when the number of the subjects change ("He walked" is the same verb form as "They walked," for example).

Why do we use subject-verb agreement?

Subject-verb agreement is very important because without it, the reader can be confused. Rule: Subjects must agree with their verbs in number. Singular subjects must take singular verbs. Plural subjects must take plural verbs.

What is the purpose of subject-verb inversion?

Subject-verb inversion has occurred in the b-sentences to emphasize the post-verb subject. The emphasis may occur, for instance, to establish a contrast of the subject with another entity in the discourse context.