The correct answer is C) Natural supply and mechanical exhaust. This is because the small passenger vessel regulations require enclosed spaces containing gasoline, machinery, or fuel tanks to have natural supply ventilation and mechanical exhaust ventilation. Natural supply ventilation allows fresh air to enter the space, while mechanical exhaust ventilation actively removes any hazardous fumes or vapors. This combination helps maintain proper air circulation and prevent the buildup of flammable or explosive gases in these enclosed areas. The other options are incorrect because they do not meet the specific ventilation requirements for these types of enclosed spaces. Option A has natural exhaust instead of mechanical, Option B has both natural supply and exhaust which is not sufficient, and Option D has mechanical supply and exhaust which is unnecessary and more complex than the required setup.