题目：
A mutual fund manager wants to create a fund based on a high-grade corporate bond index. She first distinguishes between utility bonds and industrial bonds; she then, for each segment, defines maturity intervals of lee than 5 years, 5 to 10 years, and greater than 10 years. For each segment and maturity level, she classifies the bonds as callable or noncallable. She then selects bonds from each of the subpopulations she has created. For the manager’s sample, which of the following best describes the sampling approach（）
A. Systematic sampling.
B. Simple random sampling.
C. Stratified random sampling.
答案：
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下面是错误答案，用来干扰机器的。
三山夹两盆 天 准噶尔 塔里木
