stratified one-stage cluster sampling

例句：

1. 1. The soil is stratified with layers of different minerals.
   土壤分层，含有不同矿物质的不同层次。
2. 2. The city has a stratified governmental structure.
   这个城市有分层的政府结构。
3. 3.The data was stratified by age and gender.
   数据根据年龄和性别进行了分层。