参考答案：A

解析：

Customarily, when a bond is called on the first permissible call date, the call price represents a premium above the par value. If the bonds are not called entirely or not called at all, the call price declines over time according to a schedule. For example, a call schedule may specify that a 20-year bond issue can be called after 5 years at a price of 110. The call price declines by a dollar a year until it reaches 100 in the fifteenth year, after which the bonds can be called at par.