please explain the following summary

Summary of MM Propositions Case I - no taxes or bankruptcy costs No optimal capital structure; Case II - corporate taxes but no bankruptcy costs Optimal capital structure is almost 100% debt; Each additional dollar of debt increases the cash flow of the firm; Case III - corporate taxes and bankruptcy costs I Optimal capital structure is part debt and part equity; Occurs where the benefit from an additional dollar of debt is just offset by the increase in expected bankruptcy costs