A firm currently has a debt$-$to$-$equity ratio $($D$/$E$)$ of $50\%.$ If the firm changes its debt$-$to$-$equity ratio to $40\%,$ all else constant, this change will:

a$.$ Increase the total debt level of the firm.

b$.$ Decrease the proportionate use of equity financing.

c$.$ Cause the NPV of projects under consideration to decrease.

d$.$ Decrease the firm's WACC.

e$.$ Not affect the firm's capital budgeting decisions.