If a cost-minimization firm's marginal product of labor equals 1 ton of output, while the marginal product of capital equals 7 tons of output and the cost of capital is $14 per unit, then O a. The cost of labor (wage rate) must be $2 O b. The cost of labor must be $1/7 c. The cost of labor must be $7 O d. The cost of labor must be $14 as well