sub-grade in soft clay region

例句：

1. 1. The sub-gradestudents are given extra help in mathematics.
   低年级学生在数学上获得额外的帮助。
2. 2. The sub-grade teachers weresurprised by the results of the test.
   低年级教师对考试结果感到惊讶。
3. 3. Thesub-grade students have to work harderthan their senior counterparts.
   低年级学生必须比他们的高年级同学更努力地工作。