You are presented with the question "A fire requires a by-product of what?" and the following answer choices: 
- sunlight
 - heat energy
 - electromagnetic energy
 - photosynthesis.
 - evaporation
 - heating liquids
 - Electrical energy
 - harmful substances

Now knowing that afire requires oxygen to burn and they produce oxygen as a by-product of photosynthesis, choose the best answer.


 

    photosynthesis.     