18 Let θ: R → S be a ring homomorphism. Prove each of the following statements:
(a) If R is a commutative ring, then θ(R) is a commutative ring.
(b) θ(0) = 0.
Let 1R and 1S be the identities for R and S, respectively. If θ is onto, then θ(1R) = 1S. If R is a field and θ(R) ≠ 0, then θ(R) is a field.