You did not attach any equation to this question, but you can pin point the answer if you follow this instruction.
Every chemical equation has two sides, the left side and the right side, the two side are separated by an arrow.
The left side is the reactant side, those elements or compounds that are written on that side are all reactants. So, if the CO is one of the element on that side, then the answer is reactant. The right side is the product side, all the compounds written on that side are products. Thus, if CO is on that side, then the answer is product. If it happens that CO appear on both sides, then that means that it is both a reactant and a product.