问题如下：
Which of the following choices correctly characterizes basis-point volatility and yield volatility as a function of time within the lognormal model?
选项：
Basis-point volatility
Yield volatility
A. increases constant
B. increases decreases
C. decreases constant
D. decreases decreases
解释：
Choices B and D can be eliminated because yield volatility is constant. Basis-point volatility under the CIR model increases at a decreasing rate, whereas basis-point volatility under the lognormal model increases linearly. Therefore, basis-point volatility is an increasing function for both models.
我觉得这个题目应该联想到的模型是model3，basis 算是一个时间点的，简单理解为短期的，根据model3，t小波动率大，yield就是t大波动率变小。实在看不出来可以联想到cir model，题干中没有关于r的提示
