研究者们使用死亡证明和人口普查数据作为参考资料，主要对象是20世纪初出生的人。
The study focused on people born at the beginning of the 20th century, using death certificates and census data.
研究者们使用死亡证明和人口普查数据作为参考资料，主要对象是20世纪初出生的人。
The study focused on people born at the beginning of the 20th century, using death certificates and census data.
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