Auxiliary boilers are divided into several classifications, one of which is __________.

Correct Answer: Option B — water-tube forced circulation

Auxiliary boilers are categorized by their circulation methods, including natural, forced, and controlled circulation. Forced circulation utilizes a pump to ensure positive water flow through the tubes, which is critical for preventing overheating and ensuring uniform heat transfer in high-pressure or high-heat-flux marine boiler applications under 46 CFR Subchapter F.