Final answer:
Direct immunofluorescent (DFA) assays are commonly used for detecting influenza viruses, adenovirus, and RSV.
Step-by-step explanation:
Direct immunofluorescent (DFA) assays are commonly used for detecting viral antigens from clinical material. These assays are rapid and highly specific. In the given options, DFA assays are used for detecting influenza viruses, adenovirus, and RSV. Therefore, option b, 'Influenza viruses, adenovirus, and RSV' is the correct answer.