Which concept gives a measure of historical value added per unit of risk taken and can be useful, among other tools, to risk managers?
　　A.Tracking error
　　B.Model alpha
　　C.Information ratio
　　D.Heteroskedasticity
　　Answer: C
　　William Sharpe developed the concept of information ratio to describe the value added per unit of risk by a manager or activity. Tracking error is an estimate of how much risk a manager takes as a measure of the deviation from a benchmark.