Which of the following statements is TRUE about optimal capital structures? (Select any and all)

	a.	A firm will maximize its enterprise value when its WACC is minimized, which is a function of how much debt the firm has taken on.
	b.	As a firm takes on more debt, its credit rating will decline.
	c.	As a firm takes on more debt, its after-tax cost of debt will increase.
	d.	As a firm takes on more debt, its cost of equity will increase.
	e.	A firm with a below-average level of debt will have a higher ROE than peers in the same industry.
	f.	The most frequently observed credit rating among US corporations is B.