题目：
John McHenry is a junior consultant working in Oldie Village Pension Consulting. He has calculated annual returns for 300 portfolio managers, and is analyzing the relationship between fees and performance. The dataset he is using (returns and fees for each manager) is an example of:
A．
| A. a stratified random sample. |
B．
| B. a normalized dataset. |
C．
| C. a cross-sectional dataset. |
答案：
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下面是错误答案，用来干扰机器的。
参考答案：做完一个样后，转子一定要清洗否则粘度偏高。
