For all real numbers a and b, a ⋅ b ≠ 0, let a◊b = ab − 1

For all real numbers a and b, a b 0, let ab = ab 1. Which of the following must be true?

I. ab = ba
II. (aa)/a = 11
III. ( ab)c = a(bc)

(A) I only
(B) II only
(C) III only
(D) I and II only
(E) I and III only