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, decreasing what during travel likely conserves fuel?

Choose your answer from: i. the energy of the car. ii. air mass over Earth's surface. iii. the amount of cars used. iv. the size of the wheels. v. the amount of water used. vi. kinetic energy. vii. preventing heat transfer. viii. energy usage.
The answer is:
iii.