Which of the following is NOT a true statement?

• Extendible bonds allow the issuer to extend the maturity date of the bond.
• Callable bonds give the issuer the option to "call" or repurchase outstanding bonds at predetermined call prices at specified times.
• Mortgage bonds are debt instruments that are secured by real assets.
• Retractable bonds allow the bondholder to sell the bonds back to the issuer at predetermined prices at specified times earlier than the maturity date.