When metal conducts heat , that metal expands, and steel is a solution of metals. Given these facts, when does steel expand among the following options:
- 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


 

       when it conducts heat  