Answer:
Shorten the horizontal line; bunch the five red arrows together
Explanation:
As the car rolls down the ramp, its potential energy is converted to kinetic energy. When the car reaches the flat surface, its kinetic energy is converted to thermal energy. Total energy is conserved, and the car always starts with the same amount of potential energy, so the amount of thermal energy is the same for all three trials. The red arrows indicate the amount of thermal energy, so they will stay the same. The car has a shorter stopping distance in the third trial, so the horizontal line will be shortened.