Answer:
A. Cost of funds has changed
B. Firm's risk has changed
Explanation:
The required rate of return on bonds refers to an investor's expected rate of return which is based upon rate of return other investors earn in the market on similarly priced bonds. This is also referred to as yield to maturity i.e YTM.
Coupon rate of payment of bond is the interest payment on such bonds which is usually fixed at the time of issue of such bonds.
Required rate of return may differ on account of change in cost of funds to the issuer which is cost of debt denoted as . Cost of debt is determined by tax rate and net proceeds from the issue of such bonds.
Required rate of return may also change on account of change in the firm's risk. If the firm assumes more risk, such risk would deter investors from investing in such bonds and in such scenario, the firm has to offer higher coupon rate than the rate prevailing in the market to attract the investors.