Which of the following is NOT one of the four checks done before backing?

The correct choice emphasizes that checking the fuel level is unrelated to the safety checks performed before backing up a vehicle. The primary goal of the pre-backing checks is to ensure that the area behind the vehicle is clear of obstacles and personnel to prevent accidents. This includes actions like checking behind the vehicle to look for any objects or individuals that could pose a risk, adjusting mirrors to improve visibility, and using a backup guide if available, to assist in navigating while reversing.

Fuel level checks are important for vehicle operation but do not pertain to the immediate safety and maneuverability concerns that arise when preparing to back up. Hence, option C represents an action that does not fit within the essential safety checks designated to prevent accidents during vehicle operation.