The correct answer is D) A hot boiler will continue to generate steam after the fires are secured. This is correct because even after the fires are secured, the heat stored in the boiler's metal components will continue to generate steam for a period of time. This is an important safety consideration, as the boiler must be properly shut down and cooled to prevent damage or hazardous conditions. The other answer choices are incorrect because: A) Loss of water can indeed harm a boiler if not promptly restored, B) Some boilers can continue generating steam after the fires are secured, and C) The water level in a boiler can fluctuate during normal operation.