In the Equation $R \times p _ { k } = M P K + \Delta p _ { k } , R \times p _ { k }$

In the equation $R \times p _ { k } = M P K + \Delta p _ { k } , R \times p _ { k }$ is the:

A) capital gain of capital
B) return to stock prices
C) return to capital
D) user cost of capital if taxes are zero
E) return to a bank account