Fact 1: An automobile engine transforms chemical energy into mechanical energy.

Fact 2: Mechanical energy is the sum of Kinetic Energy and Potential Energy.

Given the two facts above, answer the question "What works by summing kinetic energy and potential energy?" with the following options: 
- Riding a bike
 - transportation technology
 - adding heat
 - an automobile engine
 - circulatory systems
 - a hydraulic system
 - Thyroid-stimulating hormone
 - heterotrophs


 

    an automobile engine     