Final answer:
The Department of Veterans Affairs specifically serves military veterans, making it the agency that serves a narrow clientele compared to other options such as the Internal Revenue Service, State Department, and Department of Education.
Step-by-step explanation:
The agency that serves a narrow clientele rather than the general interests of the public among the options provided is the Department of Veterans Affairs. Government agencies like the Internal Revenue Service (IRS), State Department, and the Department of Education serve broad segments of the population with their services. The Department of Veterans Affairs, however, is dedicated to serving military veterans specifically, which is a more selective group compared to the entire public.