Choose the correct statement about allopurinol: A. It is a purine antimetabolite with antineoplastic activity B. It is a competitive inhibitor of xanthine oxidase C. It is inactive itself, but its metabolite alloxanthine is a competitive inhibitor of xanthine oxidase D. Both allopurinol as well as its metabolite alloxanthine are noncompetitive inhibitors of xanthine oxidase