Assuming all M&M assumption hold and there is no taxes, if a firm decides to increase its debt$-$to$-$equity ratio, the firm$$s weighted average cost of capital $($WACC$)$ will $\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_,$ the cost of equity will $\_\_\_\_\_\_\_\_\_\_\_\_$ and its cost of debt will $\_\_\_\_\_\_\_\_\_\_\_\_\_.$

a$.$

Decrease; increase; decrease;

b$.$

Stay the same; increase; stay the same

c$.$

Stay the same; stay the same; stay the same

d$.$

increase; increase; increase