My cousin is . . . . . . . . police officer.

The correct answer is:

D. no article

A police officer is a general term, so we do not need to use an article.

Here are some examples of how we can use the word "police officer" in a sentence:

• My cousin is a police officer.
• I saw a police officer on the corner.
• The police officer arrested the suspect.
• The police officers are investigating the crime.