Question

write down what you think is a rule that could explain what makes a sentence grammatically correct or not

Answer 1

In order for a sentence to be grammatically correct, the subject and verb must both be singular or plural.

Answer 2

In order gor a sentence to be gramatically correct, the subject and verb must both be singular and plural. In other words, the subject and verb must agree with one another in their tense. If the subject is in plural form, the verb should also be in plural form.