If (a) and (b) are non-zero non-collinear vectors such that (a ⋅ b = 0), and the angle between (a) and (b) is (theta), then if (c) is any vector satisfying (a ⋅ c = b ⋅ c = 0), what is (theta)?

a) 0°
b) 45°
c) 90°
d) 180°