Fact 1: When metal conducts heat , that metal expands.

Fact 2: Steel is a solution of metals.

Given the two facts above, answer the question "When does steel expand?" with 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  