What is the role of a "veterinarian"?

The role of a veterinarian is primarily to diagnose, treat, and care for animals that are sick or injured. This involves not only performing medical examinations and surgeries but also providing preventive care, conducting vaccinations, and advising pet owners on animal health and welfare. Veterinarians have specialized training and education that equips them to handle various medical issues specific to different animal species, which is central to their responsibilities.

In contrast, the other options describe different roles that are not aligned with the main duties of a veterinarian. A doctor who treats sick humans pertains to human medicine and does not involve animal health care. Researching animal behavior is typically the domain of ethologists or animal behaviorists, who focus on studying animals in their natural environments. A veterinary nurse does assist veterinarians, especially in surgery and handling day-to-day animal care, but this role does not encompass the full scope of responsibilities and authority that veterinarians have, including making medical decisions. Therefore, option C accurately captures the essence of what a veterinarian does in the context of animal health care.