Identify which of the following are tautologies....

Apparently a. and d. are tautologies, but I cannot understand why so I do not know how to prove either.

(8 pts) 7. Identify which of the following (if any) are tautologies regardless of P, Q and the universe of discourse for x. If the statement is a tautology prove it. Be sure to state all laws or rules of inference that you use in your proof. b. axPOx) A3xQ(x) 3x(P(x), A, Q(x))