Question

A car accelerates on a horizontal road due to the force exerted by

Answer 1

The car accelerates on a horizontal road due to the force excreted by the friction on the opposite side.
The wheels of the car apply forward force on the horizontal road, ang the friction applies the same amount of force in backward direction. The horizontal road applies force in backward direction and Moves itself back, so that the car accelerates in forward direction.

Answer 2

Engine of the car

As it's power after overcoming the rolling friction will accelerate the car further