Answer
The correct equilibrium expression is represented on alternative e).
Work Step by Step
$$K_c = \frac{[Products]}{[Reactants]}$$
Since there are 2 CO and 2 $CO_2$ in the balanced equation, both their concentrations are going to appear in the Kc expression to the power of 2.
$$K_c = \frac{[CO_2]^2}{[CO]^2[O_2]}$$
