stratification of scientists

例句：

1. 1. The city is divided into different stratified districts.
   这个城市被分成不同的分层区域。
2. 2. The soil was stratified with layers of organic matter.
   土壤被有机物质的层次所分层。
3. 3.The research team conducted a stratified sampling of the population.
   研究小组对人口进行了分层抽样。