Answer:
reaction force of the gravel pushing up against the car
Explanation:
In part A, we are told that gravity (i.e gravitional force or weight) is acting downward to hold the car downward on the gravel.
Because the car is stationary (i.e parked) and not sinking into the gravel, there must be an equal and opposite force acting upward in order to balance out the gravitational force.
This is known as the the reaction force of the gravel pushing up against the car.
