Joan Jillson Owns a Coffee Shop

Joan Jillson owns a coffee shop. Assume that the marginal product of the labor Joan employs (MP_L) equals 500 cups per week and the marginal product of her shop's capital (MP_K) equals 1,000. Assume also that the wage (w) Joan pays her workers equals $250 per week and the rental price (r) of her capital - her coffee machines - equals $500 per week. Which of the following correctly analyzes whether Joan is minimizing her costs?

A) No, Joan is not minimizing her costs because MP_K is greater than MP_L and r is greater than w.
B) Yes, Joan is minimizing her costs because MP_K/r equals MP_L/w.
C) No, Joan is not minimizing her costs because MP_L × w is less than MP_K × r.
D) Yes, Joan is minimizing her costs because she is a price-taker in the markets for labor and capital.