问题如下：
When determining the relative degree of variability of different data sets if those data sets have different means or different units of measurement, which of the following parameters is most suitable parameter?
选项：
A. Coefficient of variation.
B. Standard deviation.
C. Mean.
解释：
The relative measurement of risk is the coefficient of variation, which is more useful for measuring data sets with different mean and data sets with different unit of measurement than standard deviation or mean.
不理解题目意思，尤其是最后一句的意思？