You are presented with the question "What causes thermal expansion?" and the following answer choices: 
- Electrical energy
 - energy of moving objects
 - making an object hot
 - cooling an object
 - freezing an object
 - chemical reaction
 - global warming
 - stretching an object

Now knowing that increasing heat causes thermal expansion and heating by direct heat is usually too hot, choose the best answer.


 

   making an object hot      