Which of the following sentences demonstrates proper subject-verb agreement?

To determine which sentence demonstrates proper subject-verb agreement, we need to examine each sentence and check if the subject and verb agree in number. Here are the sentences:

1. The cat eats.
2. The cat eat.
3. The cats eats.
4. The cats eat.

To find the correct sentence, we need to make sure that the subject and verb match in number. In English grammar, singular subjects usually take singular verbs, and plural subjects usually take plural verbs.

Now let's analyze each sentence:

1. "The cat eats." - This sentence shows proper subject-verb agreement. The singular subject "cat" is paired with the singular verb "eats."

2. "The cat eat." - This sentence does not demonstrate proper subject-verb agreement. The singular subject "cat" does not agree with the plural verb "eat."

3. "The cats eats." - This sentence does not showcase proper subject-verb agreement. The plural subject "cats" does not agree with the singular verb "eats."

4. "The cats eat." - This sentence demonstrates proper subject-verb agreement. The plural subject "cats" is matched with the plural verb "eat."

In summary, the sentence that demonstrates proper subject-verb agreement is: "The cat eats."