Which of the following statements regarding provisions for paying off bonds is least likely correct（）

A. Nonrefundable bonds can be callable.

B. Serial bonds are an issue with several staggered maturity dates.

C. A sinking fund provision gives the company the option to retire portions of the bond issue prior to maturity.

伴慢性心功能不全的高血压患者宜选用

A．维拉帕米
B．硝苯地平
C．尼莫地平
D．吗啡
E．普萘洛尔