Final answer:
When backing up a vehicle, one must check the rear and the sides of the front of the vehicle to prevent collisions with any obstacles or hazards.
Step-by-step explanation:
When backing left or right, have both hands on the wheel. You need to check the rear, but also check the sides of the front of the vehicle. The correct option is (a) Sides. It is important to constantly monitor the sides of the vehicle to ensure that you are not at risk of colliding with obstacles, pedestrians, or other vehicles.