问题如下：
The Merton model is used to predict default. It builds on several very strong assumptions and its applicability is hampered by practical difficulties. Which of the following statements does not correctly identify limiting assumptions or practical difficulties of using the model?
选项： The
model relies on a simplistic capital structure with only one debt issue.
The asset value volatility cannot be estimated because firm value does not trade.
C.The model assumes that debt does not pay a coupon while most publicly traded debt is coupon debt.
D.The model assumes a constant riskless interest rate.
解释：
ANSWER: B
This statement is incorrect because the asset volatility can be recovered iteratively from the equity volatility and model prices. Other statements are correct weaknesses of this model.
1、老师，假设价格是对数，是不是蕴含的两个意思，价格连续，和大于零？
2、另外，这里是沃顿推论四求pD的假设，不是沃顿模型的假设；我看了下PPT，沃顿里面没有波动率很定，波动率很定是BSM的假设；我感觉沃顿应该只是一种资产负债表的映射方法，这种方法用到BSM用来求，Dt 和St等，所以如果题目问什么PD,LGD,Dt,St的假设，直接往BSM上去想就完了？
3、还有就是既然沃顿和BSM里面都说了，假设公司只有一种零息债；为啥沃顿的推论三还要讨论机构化债券的问题呢？
4、沃顿里面有个假设“公司的股权、债务和资产可以很容易地在市场上交易。空头仓位没有限制。”资产可以交易想得通，就是求Vt，股权不就是求出来的嘛，债券也只需要一个到期面值F？
5、莫顿的假设“均衡市场，风险补偿=miu-rf”，这个是用在哪里的啊？
