stratified single-stage cluster sampling

例句：

1. 1. The data was stratified by age and gender.
   数据按年龄和性别分层。
2. 2. The city is divided into several stratified neighborhoods.
   这个城市被分成几个分层的社区。
3. 3. The research was conducted in a stratified sample of students.
   这项研究在分层的学生样本中进行。