The correct answer is option 'A'.

Explanation:
The given sentence is in the present perfect tense, which is used to talk about actions that started in the past and are still relevant or ongoing in the present. In this case, we are talking about the police not catching the thief yet.

Subject-Verb Agreement:
In English grammar, subject-verb agreement means that the subject and verb in a sentence must agree in number. In other words, a singular subject takes a singular verb, and a plural subject takes a plural verb.

In this sentence, the subject is "police," which is a plural noun. Therefore, we need to use the plural form of the verb "to catch," which is "haven't caught."

Contractions:
The correct contraction for "have not" is "haven't." Therefore, the correct form of the verb "to catch" in the present perfect tense with a plural subject is "haven't caught."

Options Analysis:
Let's analyze the other options to understand why they are incorrect:

- Option 'B': "didn't catch" is in the simple past tense, which suggests that the action of catching the thief is already completed in the past. However, the sentence requires the present perfect tense to indicate that the action is still ongoing.

- Option 'C': "hasn't caught" is in the present perfect tense, but it uses the singular form of the verb "to catch." This is incorrect because the subject "police" is plural, and we need to use the plural form of the verb.

- Option 'D': "don't catch" is in the present simple tense, which indicates a general truth or habitual action. However, the sentence requires the present perfect tense to convey the ongoing nature of the action.

Therefore, the correct answer is option 'A': "haven't caught." This form correctly matches the plural subject "police" and conveys that the action of catching the thief is still ongoing.