If output is produced according to Q = 5Lk (L is the quantity of labor and k is the quantity of capital), the price of K is $12, and the price of L is $6, then the cost minimizing combination of K and L capable of producing 4,000 units of output is
A. L = 25 and k = 32.
B. L = 30 and k = 26.67.
C. L = 10 and k = 80.
D. L = 20 and k = 40.
E. L = 40 and k = 20.