Final answer:
The bold adjective 'heroic' describes the noun 'firefighter', highlighting the bravery and valor of the individual in the context.
Step-by-step explanation:
The question at hand asks which noun the bold adjective describes. In the context of the provided sentences, the adjective 'heroic' is used to describe the noun 'firefighter'. Therefore, the correct answer to the question is 'b) firefighter'. The heroic firefighter is covered in dirt and soot, exemplifying that the adjective 'heroic' is indeed emphasizing the brave and valiant qualities of the firefighter discussed in the narrative.