参考答案：B

解析： 词汇题。根据第一段第二句“Millions of individuals became engaged in a variety of aerobic activities，and literally thousands of health spas developed around the country to capitalize on this emerging interest in fitness， particularly aerobic dancing for females．”看来，spas前后的意思是：很多人热衷于有氧操，成千上万的spas在全国各地出现，而建造这么多spas的目的是为了从这场健身运动中获利。由此可见，B是正确答案。