问题如下：
Which type of sovereign bond has the lowest interest rate risk for an investor?
选项：
A.Floaters
B.Coupon bonds
C.Discount bonds
解释：
A is correct.
Floaters are bonds with a floating rate of interest that resets periodically based on changes in the level of a reference rate, such as Libor. Because changes in the reference rate reflect changes in market interest rates, price changes of floaters are far less pronounced than those of fixed-rate bonds, such as coupon bonds and discount bonds. Thus, investors holding floaters are less exposed to interest rate risk than investors holding fixed-rate discount or coupon bonds.
A选项是浮动利率债券。浮动利率的久期为重置期的一半，接近零。Floater’s duration is half of reset period.因此浮动利率债券的利率风险最小。
老师 答案里的duration 视频里何老师没有提及 应该怎么理解？
