The correct answer is B) keep the boat afloat if flooded. Air tanks in a lifeboat are designed to provide additional buoyancy to the boat, allowing it to remain afloat even if the boat's hull becomes damaged and takes on water. The air tanks are sealed compartments that are filled with air, and they act as a backup buoyancy system to ensure the lifeboat can continue to support the weight of the occupants and supplies in an emergency situation. The other answer choices are incorrect because the air tanks do not primarily function to add strength to the boat (A), make the boat float higher (C), or provide stowage space for provisions (D). Their primary purpose is to provide the necessary buoyancy to keep the lifeboat afloat if it becomes flooded.