Answer:
1) A, that one person is pushing the car using his/her less force while B, there are two people pushing the car combining their force to let the car move forward.
2) The car at picture b is accelerating because of the amount of force those two people pushing it. As those two person pushing it together the acceleration of the car increases.
3) The relation of the net force and acceleration are acting on the system, each of the force adds to produce a net force causing it to move of what direction they are pushing.
Explanation:
Hope this helped :D
