In the Notation of the Book,K = (1 − λ)K_l

In the notation of the book,K = (1 − λ) K_l + λ(1 − τ) i ; which of the following is correct?

A) The debt-to-equity ratio is λ
B) The cost of equity capital for a levered firm is K_{l
C) The after-tax cost of debt capital is i
D) all of the options}