NO.PZ2020033001000072
问题如下：
Within the log-normal model, how are basis-point volatility and yield volatility changing over time ?
选项：
Basis-point volatility
Yield volatility
increases
constant
increases
decreases
decreases
constant
decreases
decreases
解释：
A is correct.
考点：Log-normal model
解析：
In Log-normal model, basis-point volatility increases linearly and yield volatility is constant.
basis point是不是是指每一步的波动的变化，在model4里面，每一次波动的变化是σ*r，
yield volatility指的是这个模型本身的波动率，在这些模型里 都是固定的σ？
