class 含义广泛，指人或物按优劣划分的等级，也指学校中的年级或班级。
degree 指程度、范围不同，社会地位的高低。也可指形容词或副词的级。
grade 指按地位或优劣划分的等级，既可指人又可指物。
rank 指人在社会中的地位或等级，尤指军队中的军衔。
参考例句
1. Potatoes are graded according to size and quality. 马铃薯按大小和质量分等级。
2. Are you in Grade Four? 你们是四年级的吗？
3. For me, I rather make the top grade in 20 competitions, but is not supports 40 reluctantly. 对我来说，我宁愿在20场比赛中打出顶级水平，而不是勉强支撑40场。
英英解释
n.
1. a body of students who are taught together
2. a relative position or degree of value in a graded group
3. the gradient of a slope or road or other surface
4. one-hundredth of a right angle
5. a degree of ablaut
6. a number or letter indicating quality (especially of a student's performance)
7. the height of the ground on which something stands
8. a position on a scale of intensity or amount or quality
9. a variety of cattle produced by crossbreeding with a superior breed v.
1. assign a rank or rating to
2. level to the right gradient
3. assign a grade or rank to, according to one's evaluation
4. determine the grade of or assign a grade to
