问题如下：
A risk manager is considering switching from using
historical volatility to using implied volatility in VaR calculations. Which of
the following statements about implied volatility is correct?
选项：
A. Implied volatility estimates are model dependent and a
misspecified model can result in erroneous forecasts.
B. Implied volatility estimates require that historical
returns are indicative of future returns.
C. Implied volatility estimates tend to underestimate
future volatility as a result of mean reversion.
D. Implied volatility estimates are generally accurate
even if there is only one trade in the option used to calculate an estimate.
解释：
B选项描述的是historical-based approach的特点，B错误。implied-volatility-based-approach中没有mean reversion的假设，C错误。D选项描述的情况，option value的估计就不靠谱，那么反求出来的implied volatility也肯定是不准确的，D错误。
