市场研究人员常常按年龄和社会阶层划分人口。
Market researchers often segment the population on the basis of age and social class.
当然，对人口年龄结构的划分是相对的，而不是一成不变的。
Of course, the division of population age structure is comparative, but not invariable.
这些划分规则中至少要包含一条：该州的每个选区必须有同样的人口。
The rules include only that each district in the state must contain the same population.
这些划分规则中至少要包含一条：该州的每个选区必须有同样的人口。
The rules include only that each district in the state must contain the same population.
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