A firm has mortgage bonds with a $5\%$ coupon rate. The risk of the firm has increased, raising the yield on the mortgage bonds to $7\%.$ They plan to issue additional debt as debentures, which will have a lower credit rating than the mortgage bonds. Which of the following is true?

A$.$ The debentures will also have a $5\%$ coupon rate.

B$.$ The debentures will have a $7\%$ coupon rate due to higher firm risk.

C$.$ The debentures will have a coupon rate above $7\%$ due to the higher risk and lower credit rating.

D$.$ The debentures will have a coupon below $5\%$ because of their relationship with the investment bank.