The correct answer is C. Fuel tanks should not be topped off with no room for expansion. This is because leaving room for fuel expansion is an important safety precaution during fueling. Overfilling the tank can cause fuel to spill out, which poses a serious fire hazard. Regulations require leaving enough space in the tank to allow for thermal expansion of the fuel as it warms up. The other answer choices are correct precautions during small craft fueling: having a fire extinguisher nearby, shutting down all engines/motors, and closing all openings to prevent vapors from escaping. But topping off the tank with no expansion room is an unsafe practice that should be avoided.