The answer is C.
The reactants are charcoal that is unlit + oxygen and the products are the burnt charcoal + energy.
So for every combustion reaction like this one, CxHy is the wood. So before you light the wood, it is actally a reactant together with oxygen, because without oxygen the wood will not burn. So under the influence of heat, wood produces substances like carbon dioxide and heat, the moment you see wood burning it it already producing products, CO2 and heat (which is the fire). This is a combustion reaction.
Combustion reaction is exothermic because it releases energy.