A company is planning a $50 million expansion. The expansion is to be financed by selling $20 million in new debt and $30 million in new common stock. The before-tax required return on debt is 9 percent and 14 percent for equity. If the company is in the 40 percent tax bracket, what is the marginal weighted average cost of capital（）

A. 10.6%.

B. 9.0%.

C. 10.0%.

下图左侧表示健康人体内甲状腺激素的分泌调节，右侧表示Graves氏病的致病机理，该病是由于机体产生一种抗体，它可与B激素受体结合，从而发挥与B激素相同的生理作用，但甲状腺激素不会影响该抗体的分泌。请回答：

图中的激素A能促进激素B的分泌，进而促进甲状腺激素分泌；当甲状腺激素达到较高水平时，又会造成有关腺体分泌的（）（填图中字母）减少，进而使甲状腺激素的分泌减少。这两个过程反映了健康人体内甲状腺激素的分泌存在（）调节，也存在着（）调节。