The correct answer is B) shutting all sources of air into the compartment. Shutting off all sources of air to the compartment on fire is the best way to bring the fire under control with minimal impact on the vessel's stability. This prevents the fire from spreading and consuming more oxygen, which could lead to a potentially destabilizing loss of buoyancy if the compartment were to be flooded. The other options are not as effective for controlling the fire with minimal stability impact. Cooling the outside bulkheads (A) may not address the root cause of the fire, flooding the compartment (C) could significantly impact stability, and closing the sea chest (D) does not directly address the fire itself.