例句：
Dust masks are graded according to the protection they offer
防尘口罩根据它们的防护效果分等级。
Milk is sold in grades.
牛奶是分等级出售的'。
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？
All the materials used were of the highest grade.
使用的材料全是优质品。
You get an A grade for scores of 75 and over.
75分及75以上的分数就是优等。
