问题如下：
In risk management, many risk indicators need to be calculated. Which of the following risk indicators is used the least frequently?
选项：
A.ES measures.
B.Semi-variance measures.
C.VaR measures.
D.Distorted risk measures.
解释：
D is correct.
考点：Defining and Calculating Risk Measures
解析：Expected Shortfall，Value at Risk都是常用的风险指标，半方差用的频率也不是很低。较少使用的是Spectral and distorted risk measures。
半方差法 是什么。。。
