class number of a rational simple algebra

例句：

1. 1. She is a teacher in the first class.
   她是一名一年级的老师。
2. 2. The students are divided into different classes.
   学生们被分成不同的班级。
3. 3. Class size can vary greatly depending on the school.
   班级规模可以根据学校而有很大的变化。