How to balance chemical equations? 

Apply the Law of Conversetion of Mass to get the same number of atoms of every element that appears in only one reactant and product.
Once one element in balanced, proceed to balance another, and another, until all elements are balanced.

How to balance a chemical equation A chemical equation is a theoretical way to represent what happens during a chemical reaction. The conversation of law says that no atom of matter can not be created or destroyed during a chemical reaction. The number of atoms present in the reactants at the beginning should be the same as the number of atoms present in the product at the end . With this guide you 'll learn how to balance a chemical equation.

Combustion is the act or process of burning. therefore, i believe the answer is  a: burning wood.