Equilibrium constant Kp for following reaction : $MgCO_3(s)\rightleftharpoons MgO(s)+CO_2(g)$

Question

( A ) $K_P = \frac{P_{CO_2} + P_{MgO}}{P_{MgCO_3}}$
( B ) $K_P = \frac{P_{MgCO_3}}{P_{CO_2} \times P_{MgO}}$
( C ) $K_P = P_{CO_2} \times \frac{P_{CO_2 \times P_{MgO}}}{P_{MgCO_3}}$
( D ) $K{_P}=P_{CO_2}$