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2.There are two main ways to define a middle class: in relative terms, as the middle income range of each country; or in absolute terms, using a fixed band for all countries.
主要有两种方法来界定中产阶级：相对值计算法——各国的中等收入范围；或者，绝对值计算法——用一个确定的值域衡量所有的国家。
