Fact 1: Carpooling decreases the amount of cars used to travel to a place.

Fact 2: Arrange carpools to conserve fuel.

Given the two facts above, answer the question "Decreasing what during travel likely conserves fuel?" with the following options: 
- the energy of the car
 - air mass over Earth's surface
 - the amount of cars used
 - the size of the wheels
 - the amount of water used
 - kinetic energy
 - preventing heat transfer
 - energy usage


 

   the amount of cars used      