Provide the K_eq expression for the given acid-base equation. (Use the letters as expression terms.)

Equilibrium constant expression: Keq = [A]*[B]/[C]*[D].

Alternative equilibrium constant expression: Keq = [A]*[C]/[B]*[D].

Another equilibrium constant expression: Keq = [C]*[D]/[A]*[B].

Final equilibrium constant expression: Keq = [A]*[D]/[B]*[C].

Provide the Keq expression for the given acid-base equation. (Use the letters as expression terms.)