Final answer:
The longest stage of a fire is typically the smouldering stage, where combustion occurs slowly and at low temperatures, often preceding the flaming stage.
Step-by-step explanation:
According to the textbook, the typically longest stage of a fire is b. the smouldering stage. The smouldering stage is a combustion process that occurs at a surface without flame and at a low temperature. It often involves a slower oxidation process and can continue for an extended period before either dying out or transitioning into the flaming stage.