Determine which of the following functions are one-to-one. A. ƒ : R³ → R³ defined by f(x, y, z) = (x + y, y + z, x + z). B. ƒ : R² → R² defined by ƒ(x, y) = (x + y, 2x + 2y). C. ƒ : R → R defined by ƒ(x) = x³ – x. D. ƒ : R³ → R³ defined by f(x, y, z) = (x − y, y — z, x — z). E. ƒ : R → R defined by ƒ(x) = x³.