问题如下：
A large, international bank has a trading book whose size depends on the opportunities perceived by its traders. The market risk manager estimates the one-day VAR, at the 95% confidence level, to be USD 50 million. You are asked to evaluate how good a job the manager is doing in estimating the one-day VAR. Which of the following would be the most convincing evidence that the manager is doing a poor job, assuming that losses are identical and independently distributed (i.i.d.)?
选项：
A.Over the past 250 days, there are eight exceptions.
B.Over the past 250 days, the largest loss is USD 500 million.
C.Over the past 250 days, the mean loss is USD 60 million.
D.Over the past 250 days, there is no exception.
解释：
D is correct. We should expect exceptions on average. Having eight exceptions is too few, but the difference could be due to luck. Having zero exceptions, however, would be very unusual, with a probability of , which is very low. This means that the risk manager is providing VAR estimates that are much too high. Otherwise, the largest or mean losses are not directly useful without more information on the distribution of profits.
不太理解这道题的点。1) 比如选项A的8个，和basel committee的three zones的5-9个exception是什么关系呢？8个落在yellow的范围之内，不也表示模型不好么？
2) 看了关于选项D的解释，没有exception尽管可能是个小概率，但如事实如此，难道不应该理解成模型很好么？
