Which of the following statements is always true for any vectors a=axi^+ayj^+azk^ and b=bxi^+byj^+bzk^?
(a) The z-component of a−b equals bz−az.
(b) The y-component of a−b equals ay−by.
(c) ∣a+b∣=∣a∣+∣b∣.
(d) The x-component of a−b equals ax+bx.