Which of the following would reduce a firm's WACC after tax?

a. A firm issues bonds and uses the proceeds to repurchase stock.

b. A firm issues shares and uses the proceeds to pay off a bank loan.

c. A firm significantly improves its operating cost control to boost profits.

d. A firm invests in an average-risk project using equity, rather than debt financing.

e. A supermarket chain decides to establish hardware stores which increases its systematic risk.