You are presented with the question "When does steel expand?" and the following answer choices: 
- matter vibrating
 - when it loses heat
 - It gets heated up
 - flow of electrons
 - when it transfers heat away
 - recovery time from fatigue
 - when it conducts heat
 - when it cools down

Now knowing that when metal conducts heat , that metal expands and steel is a solution of metals, choose the best answer.


 

       when it conducts heat  