Which of the following is incorrect when firms use only labor and capital as their inputs in production?

a) As output doubles long-run cost of production always doubles regardless of the production functions

b) As we take the partial derivative of the long-run cots function with respect to the price of labor, we always obtain the conditional demand of labor

c) As we take the partial derivative of the long-run costs function with respect to the price of capital, we always obtain the conditional demand of capital

d) As price of labor (w) and price of capital (r) double, long-run cost always regardless of the production functions