Final answer:
Dr. McEwan is likely works for a nonprofit health organization, focusing on public health advocacy and promoting healthier lifestyles in line with global efforts highlighted by the World Health Organization.
Step-by-step explanation:
Dr. McEwan's work, which involves giving talks at community centers to encourage people to stop smoking and eat healthier, suggests that he is associated with the health industry. Given the options provided, the most suitable answer would be that Dr. McEwan works for a nonprofit health organization. These types of organizations typically focus on public health advocacy and education, working to improve community health through various programs and initiatives. The work of the World Health Organization (WHO), since its establishment in 1948, has highlighted the importance of lifestyle choices, such as diet, in preventing chronic diseases and improving longevity, hence the proliferation of diets like the Mediterranean and paleo diets. Dr. McEwan's efforts align with the goals of nonprofit health organizations, which aim to promote well-being and prevent illness rather than generate profit.