Fact 1: Increasing heat causes thermal expansion.

Fact 2: Heating by direct heat is usually too hot.

Given the two facts above, answer the question "What causes thermal expansion?" with the following options: 
- Electrical energy
 - energy of moving objects
 - making an object hot
 - cooling an object
 - freezing an object
 - chemical reaction
 - global warming
 - stretching an object


 

   making an object hot      