A written construction contract, under which Contractor agreed to build a new house for Owner at a fixed price of $200,000, contained the following provision: Prior to construction or during the course thereof, this contract may be modified by mutual agreement of the parties as to "extras" or other departures from the plans and specifications provided by Owner and attached hereto. Such modifications, however, may be authorized only in writing, signed by both parties. During construction, Contractor incorporated into the structure overhanging gargoyles and other "extras" orally requested by Owner for orally agreed prices in addition to the contract price. Owner subsequently refused to pay anything for such extras, aggregating $30,000 at the agreed prices, solely on the ground that no written, signed authorization for them was ever effected. If Contractor sues Owner on account of the "extras," which, if any, of the following will effectively support Owner's defense? I. The parol evidence rule. II. The preexisting duty rule. III. Failure of an express condition. IV. The statute of frauds. 
I and III only. I and IV only. II and IV only. Neither I, II, III, nor IV. 