Select all that are true regarding capital structure:

Question $5$ options:

a$)$

Debt repurchases $($retirement$)$ decrease the WACC

b$)$

Repurchase of common stock changes the WACC

c$)$

The cost of debt is a linear function of a firm's debt ratio

d$)$

The cost of debt increases as the proportion of debt increases

e$)$

Taxes have a proportionate effect on the WACC $($i$.$e$.,$ taxes affect all parts of the WACC in proportion$).$