Fact 1: High temperatures can cause an object to combust.

Fact 2: Combustion requires oxygen to burn.

Given the two facts above, answer the question "Applying high temperature in the presence of what can cause an object to burn/" with the following options: 
- heat
 - toxins
 - energy
 - oxygen
 - sweating
 - Energy.
 - Pollution
 - expand


 

    oxygen     