grade periodicitytechnique

例句：

1. 1. The students are in different grades.
   学生们处于不同的年级。
2. 2. This course is designed for advanced students only.
   这门课程只面向高级学生。
3. 3. The teacher gave a grade of A+ to the student's work.
   老师给学生的作业打了A+的分数。