Which of the Following Is the Equilibrium Expression for the Scrubbing

Which of the following is the equilibrium expression for the scrubbing reaction of calcium oxide and sulfur dioxide to remove sulfur dioxide from the exhaust gases of coal-fired power plants?
CaO(s) + SO₂(g) $\leftrightarrows$ CaSO₃(s)

A) K_c = [SO₂]
B) $K _ { c } = \frac { 1 } { \left[ \mathrm { SO } _ { 2 } \right] }$
C) K_c = [CaO] + [SO₂]
D) $K _ { \mathrm { c } } = \frac { \left[ \mathrm { CaSO } _ { 3 } \right] } { \left[ \mathrm { SO } _ { 2 } \right] [ \mathrm { CaO } ] }$
E) K_c = [CaSO₃] - [CaO] - [SO₂]