问题如下：
David Lok has estimated the probability of default of bond B1 to be 1.50%. He is presenting the approach the research team used to estimate the probability of default. Which of the following statements is Lok likely to make in his presentation if the team used a reduced-form credit model?
选项：
A.Option pricing methodologies were used, with the volatility of the underlying asset estimated based on historical data on the firm's stock price.
B.Regression analysis was used, with the independent variables including both firm-specific variables, such as the debt ratio and return on assets, and macroeconomic variables, such as the rate of inflation and the unemployment rate.
C.The default barrier was first estimated followed by the estimation of the probability of default as the portion of the probability distribution that lies below the default barrier.
解释：
B is correct. Statement B is correct because a reduced-form credit model involves regression analysis using information generally available in the financial markets, such as the measures mentioned in the statement.
Statement A is incorrect because it is consistent with the use of a structural-form model and not a reduced-form model. It is a structural-form model that is based on the premise that a firm defaults on its debt if the value of its assets falls below its liabilities and that the probability of that event has the characteristics of an option.
Statement C is incorrect because it is consistent with the use of a structural-form model and not a reduced-form model. A structural-form model involves the estimation of a default barrier, and default occurs if the value of firm's assets falls below the default barrier.
想问下选项C的意思和答案里的解释，没懂C选项。
