a layer or a series of layers of rock in the ground
岩石层
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a stratum of flint .燧石层。
a thin layer within any structure
层
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thin strata of air .薄薄的空气层。
a level or class to which people are assigned according to their social status, education, or income
社会阶层
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members of other social strata .其他社会阶层的成员。
【统计】 (人口的)分层抽样群体。
"late 16th cent. (in the sense ‘layer or coat of a substance’): modern Latin, from Latin, literally ‘something spread or laid down', neuter past participle of