问题如下：
A fund manager Oliver wanted to figure out the size of steel companies(measured by revenue) which distributed in a specified state in US, and their use of derivatives. The sample size is 16. He intended to use the derivatives to hedge one of three types of risk explosure:interest rate risk, exchange risk and credit risk. To explore the relationship between derivatives usage and size, Oliver can use:
选项：
A. a parametric test only.
B. a nonparametric test only.
C. both parametric and nonparametric tests.
解释：
B is correct. Although the revenue is measured on a ratio scale, scope of risk explosure is measured on only an ordinary scale. Besides, the sample size is small. Oliver thus employed nonparametric statistics to explore the relationship between derivatives usage and size.
老师好，这道题不是很理解，能否详细解释下？