几年级学的单词

例句：
1、Why get upset just because you got one bad grade?
何必因为一次成绩不好就想不开呢？
2、All the materials used were of the highest grade.
使用的材料全是优质品。
3、You get an A grade for scores of 75 and over.
75分及75以上的分数就是优等。