A student has 5 small carts, each with a different mass. Placing each of them on a flat, smooth ramp she uses a spring driven plunger to push each cart with a constant force. She measures the amount of time it takes each cart to reach the end of the ramp. She adjusts the amount of force used each time until each of the carts reach the end of the ramp with the same time. This means that each cart will have approximately the same initial acceleration. Which of the graphs below could represent the amount of force needed to push the different carts so they get the same acceleration?