Subject-verb agreement is an essential grammar rule that ensures that a sentence makes sense and is grammatically correct. This basic rule of grammar refers to the matching of the subject with its corresponding verb in terms of number and person. In simpler terms, singular subjects take singular verbs, and plural subjects take plural verbs.

Here is an example of subject-verb agreement:

Singular subject + singular verb:

The cat chases the mouse.

Plural subject + plural verb:

The cats chase the mice.

In the above examples, the singular subject `cat` takes the singular verb `chases,` while the plural subject `cats` takes the plural verb `chase.`

However, it is important to note that there are instances where subject-verb agreement can be tricky. For example, when a sentence has compound subjects, the verb must agree with the subject closest to it.

Compound subject + singular verb:

Bread and butter is my favorite breakfast.

In the above example, `bread` and `butter` are the compound subjects, but they are considered singular because they are used together as `bread and butter.` Therefore, the singular verb `is` is used instead of the plural `are.`

Compound subject + plural verb:

Sarah and her friends are going to the cinema.

In the above example, `Sarah` and `her friends` are the compound subjects, and since they are plural, the plural verb `are` is used.

In conclusion, subject-verb agreement is an essential grammar rule to ensure that your sentences are grammatically correct. Always remember to make sure that the verb agrees with the subject in terms of number and person. By following this simple rule, you can improve the clarity and coherence of your writing.