短语词组短语stratify sampling 分层抽样;分层取样stratify y 成层;分层development stratify 发展战略stratify strat 成层Stratify by 分层变量stratify analysis 叉生分析stratify vector 分层向量Stratify being sifted out 分层淘汰risk assessment stratify 危险度分级 返回 stratify