Final answer:
The masseter muscle's action is chewing, which involves elevating the mandible to break down food.
Step-by-step explanation:
The masseter is a muscle that is essential for the process of mastication, commonly known as chewing. This muscle, located in the jaw, plays a crucial role in the movement of the mandible, enabling the grinding and breaking down of food. When the masseter contracts, it elevates the mandible (lower jaw) bringing it in contact with the maxilla (upper jaw), which allows for the act of chewing. Therefore, out of the given options:
- swallowing
- chewing
- moving the lips
- closing the eye
The correct action of the masseter muscle is option b. chewing.