True or false? a) A formula can be a contradiction and contingent at the same time. _________ b) We can use propositional logic to determine whether an inductive argument is cogent. _________ c) A formula is a tautology when it always comes out true, no matter what combination of truth values we assign to the simple statements within it. _________ d) Two formulas are logically equivalent if and only if there is at least one row on a truth table where both formulas come out true. _________ e) Two formulas are logically contradictory if and only if they have opposite truth values on every row of a truth table. _________