Use propositional logic to prove the following argument is valid. Use the letters A, S, C to define the propositions. "If the ad is successful, then the sales volume will go up. Either the ad is successful or the store will close. The sales volume will not go up. Therefore, the store will close". Solution: a) Define your propositions: A = " " S = " " C = " " b) Write down the argument: c) Proof