59. The units of the integral domain of Gaussian integers are (A) +1 (B) ti (C) Both (A) and (B) (D) None of these 60. Let G be the group of all 2 x 2 non-singular matrices over the reals. Then center of G, Z (G) is a 0 (A) (B) :acR a 0) (C) 0 :a eR (D) None of these