问题如下：
Suppose the weighted average cost of capital of the Gadget Company is 10 percent. If Gadget has a capital structure of 50 percent debt and 50 percent equity, a before-tax cost of debt of 5 percent, and a marginal tax rate of 20 percent, then its cost of equity capital is closest to:
选项：
A.12 percent.
B.14 percent.
C.16 percent.
解释：
C is correct.
Using Equation 1 from the reading:
0.10 = (0.50)(0.05)(1 – 0.20) + (0.50)
= 0.16 or 16 percent
re=r0+（r0-rd）×（1-t）×d/e老师这个公式的r0是不是一个常量？即100%股权融资的要求回报率，不会因为D/E的变化而变化对吗？
