ANSWER: (C) Sentinel surveillanceREF: Park 20th edition page 38The word surveillance is the French word for "watching over"Sentinel surveillance is useful for answering specific epidemiologic questions because sentinel sites may not represent the general population or the general incidence of disease, they may have limited usefulness in analyzing national disease patterns and trends. (REF: http://www.usaid. gov/our_work/global_health/id/surveillance/sentinel.html)SURVEILLANCE:Continuous scrutiny of factors that determine the occurrence and distribution of diseases and other conditions of ill healthTypes:1. Active Surveillance:* One way to overcome the limitations of passive surveillance and get a better picture of disease burden in the community is for health workers to visit health facilities and communities to seek out cases. This is known as active surveillance.Eradication and elimination programmes may require a very active surveillance programme aimed at detecting every case.During outbreak situations surveillance must be intensified with the introduction of active case findingPassive Surveillance:Passive surveillance yields only limited data because many sick people do not visit a health facility and because those cases that do show up may not be correctly classified, recorded, or reportedSentinel Surveillance:A method of identifying the missing cases and thereby supplementing the notified casesFor example, in HIV/AIDS surveillance the proportion of the population positive for HIV7 must be monitored as well as the number of new cases of AIDS. This requires special HIV seropre vale nee surveillance usually done in a few representative sites ('sentinel surveillance").