问题如下：
Ann wants to measure the relationship between bond price and yield for an option-free based on the duration. When the yield decreases, the estimation of price increment will be:
选项：
A. smaller.
B. larger.
C. either smaller or larger.
解释：
A is correct.
The relationship between bond price and yield for an option-free bond is convex while duration is a linear measurement. So the estimation of price increase just based on duration will be smaller than the actual price increase if the yield decreases.
涨多跌少，yield减少，price不是增加的更多吗？
