问题如下：
In backtesting a value at risk (VaR) model that constructed using a 95% confidence level over a 255-day period, how many exceptions are forecasted?
选项：
A.5.00.
B.7.55.
C.12.75.
D.15.00.
解释：
C is correct. (1 -0.95) x 255 =12.75
这题95%的置信区间，不是应该双尾检验，然后算出来是2.5%*N吗
