Final answer:
A. Staffing a flu immunization clinic at a senior citizen's center. The best example of a primary care prevention strategy regarding the flu is staffing a flu immunization clinic at a senior citizen's center.
Step-by-step explanation:
The best example of a primary care prevention strategy regarding the flu is A. Staffing a flu immunization clinic at a senior citizen's center. This intervention focuses on providing access to flu vaccinations for a specific population, which is a key aspect of primary prevention. By staffing a flu immunization clinic at a senior citizen's center, healthcare professionals can ensure that older adults, who are at a higher risk of developing complications from the flu, have easy access to the flu vaccine.