If a Firm Faces Perfectly Competitive Product and Factor Markets

If a firm faces perfectly competitive product and factor markets and the marginal product of labor and capital are 4 and 9, respectively, while the wage rate is $2 and the rental rate on capital is $4, the firm should

A) use relatively more labor.
B) use relatively less labor.
C) increase all inputs proportionately.
D) decrease all inputs proportionately.