Final answer:
The word 'exhorted' best completes the sentence, conveying the action of urgently encouraging people to evacuate a building in the context of a fire.
Step-by-step explanation:
The correct word to fill in the blank is "exhorted," which means to strongly encourage or urge someone to do something. In the context given, the sentence should read: "The fireman exhorted people to evacuate the building." The words "superfluity," "intangibles," and "apathy" do not fit the context of the sentence as they do not convey the action of urging or encouraging that is required here.