Which of the following statements is correct? O a. Convertible bonds give bond issuers rights to convert bonds to common shares. O b. Retractable bonds give bond issuers rights to extend the maturity of the bond. O c. Callable bonds give bond holders rights to retire the bonds before the maturity date. O d. Assuming a flat yield curve - a coupon bond is sold at par when its current yield equals to its coupon rate. O e. Zero-coupon bonds can be sold at a premium as long as the interest rate is non-negative