为什么说C是CIR模型的缺点呢？

NO.PZ2020033001000073 问题如下 Whiof the following statements is aantage of the CIR mol? A.ring perio of high inflation, basis-point volatility creases. B.Interest rates are always non-negative. C.Out-of-the money option prices mffer with the use of normor lognormstributions. Long-run interest rates mnot hover arouna mean-reverting level. B is correct.考点CIR mol解析Basis-point volatility increases ring perio of high inflation.It is a saantage of CIR mol. CIR mol is a mean-reverting mol. 如题

NO.PZ2020033001000073问题如下Whiof the following statements is aantage of the CIR mol?A.ring perio of high inflation, basis-point volatility creases.B.Interest rates are always non-negative.C.Out-of-the money option prices mffer with the use of normor lognormstributions.Long-run interest rates mnot hover arouna mean-reverting level.B is correct.考点CIR mol解析Basis-point volatility increases ring perio of high inflation.It is a saantage of CIR mol. CIR mol is a mean-reverting mol.B为什么是对的？

NO.PZ2020033001000073问题如下Whiof the following statements is aantage of the CIR mol?A.ring perio of high inflation, basis-point volatility creases.B.Interest rates are always non-negative.C.Out-of-the money option prices mffer with the use of normor lognormstributions.Long-run interest rates mnot hover arouna mean-reverting level.B is correct.考点CIR mol解析Basis-point volatility increases ring perio of high inflation.It is a saantage of CIR mol. CIR mol is a mean-reverting mol.不明白第三个说的是什么？谢谢

NO.PZ2020033001000073 问题如下 Whiof the following statements is aantage of the CIR mol? A.ring perio of high inflation, basis-point volatility creases. B.Interest rates are always non-negative. C.Out-of-the money option prices mffer with the use of normor lognormstributions. Long-run interest rates mnot hover arouna mean-reverting level. B is correct.考点CIR mol解析Basis-point volatility increases ring perio of high inflation.It is a saantage of CIR mol. CIR mol is a mean-reverting mol. 老师您好我有点不明白为什么它是非负的。前一半让他能够均值回归，后一半有个根号r，这是非负的，但是后一半里面也有个ε，这个东西在正负一这样变化，也能够让变成负的？我有点混乱，也可能理解有什么偏差，麻烦老师解答谢谢

NO.PZ2020033001000073 问题如下 Whiof the following statements is aantage of the CIR mol? A.ring perio of high inflation, basis-point volatility creases. B.Interest rates are always non-negative. C.Out-of-the money option prices mffer with the use of normor lognormstributions. Long-run interest rates mnot hover arouna mean-reverting level. B is correct.考点CIR mol解析Basis-point volatility increases ring perio of high inflation.It is a saantage of CIR mol. CIR mol is a mean-reverting mol. 如题，请问这个波动项里面这个根号r，是用的r0还是rt？这点好像老李在课上没讲。