Consider the Following Equation for the Project WACC with a Fixed

Consider the following equation for the project WACC with a fixed debt schedule: r_wacc = r_U - dτ_c[rD + f(r_U - r_D) ]
The term d in this equation represents

A) a measure of the permanence of the debt level.
B) the annual adjustment percentage to the amount of debt.
C) the debt-to-value ratio.
D) the dollar amount of debt outstanding.