Since you can only change the amount of reactants, you should be looking for compounds on the reactant side that contain oxygen. If you decrease something on the reactant side, compounds produced on the product side will be affected. Since both CO2 and H2O contain oxygen, and the O2 is the only reactant with oxygen in it, then the amount of CO2 and H2O will be reduced.
Science fiction helps us find the answers to our problems in the stars of distant galaxies, in the minds of machines brought to life, and in the strength of the heroes who rise above adversity and save their worlds.
