这一群体还包括一些中等收入国家，如中国和尼日利亚。
This group also includes some middle-income countries, such as China and Nigeria.
第二种是“现代社会”，覆盖了大多数的中等收入水平国家。
The next is "modern society", which covers the majority of middle-income countries.
第二种是“现代社会”，覆盖了大多数的中等收入水平国家。
The next is "modern society", which covers the majority of middle-income countries.
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