The Base Ionization Constant K_b Describes Which of the Following

The base ionization constant K_b describes which of the following reactions for a weak base, B, in aqueous solution?

A) B(aq) + H^-(aq) ⇄ BH⁺(aq)
B) B(aq) +H₃O⁺(aq) ⇄ BH⁺(aq) + H₂O(l)
C) B(aq) + H₂O(l) ⇄ BH⁺(aq) + OH^--(aq)
D) B(aq) + OH^-(aq) ⇄ BH⁺(aq) + O^{2 -}(aq)
E) BH⁺ (aq) +OH^-(aq) ⇄ B(aq) + H₂O(l)