Final answer:
The buccinator muscle is located in the cheek and helps in various facial expressions and the act of chewing. Option D.
Step-by-step explanation:
The buccinator muscle is located in the cheek. Its main function is to compress the cheek, which helps in facial expressions such as whistling, blowing, and sucking, as well as in the act of chewing. When you whistle or chew, the buccinator muscle contracts to assist in these actions.
Notably, this muscle does not relate to the buttocks, chest, or bladder. Therefore, the correct answer to the question is D. cheek.