7. For each of the statements below state whether it is True or False. If True then give a proof. If False then explain why, e.g., by giving a counterexample. (a) The difference of any two odd integers is odd (b) Let a and b be integers. If a+ b is even, then either a or b is even. (c) For all positive integers n, it holds that n is even if and only if 3n2+8 is even. (d) For all positive z,y e R, if z is irrational and y is irrational then r +y is irrational. (e) Vx,yeR, if is irrational and y is rational then ry is irrational