Fact 1: Increasing heat causes thermal expansion.

Fact 2: Heat is caused by molecules moving.

Given the two facts above, answer the question "What causes causes thermal expansion?" with the following options: 
- molecules moving
 - kinetic energy
 - Electrical energy
 - Evaporation
 - molecules stopping
 - sunlight
 - molecules slowing down
 - molecules standing still


 

 molecules moving        