Let p q represent the argument we intend to prove. Which of the following is true? O a. In backward reasoning we start with p and conclude p. O b. In backward reasoning we start with p and conclude p. Oc. In backward reasoning we start with p q and reach contradiction O d. If we know for a fact that q is tautology, we may simply use a trivial proof. Oe. Ifp = T is a fact, we may simply use a vacuous proof