grade是可數名詞嗎

　　Dust masks are graded according to the protection they offer

　　防塵口罩根據它們的防護效果分等級。

　　Milk is sold in grades.

　　牛奶是分等級出售的。

　　Why get upset just because you got one bad grade?

　　何必因為一次成績不好就想不開呢？

　　All the materials used were of the highest grade.

　　使用的材料全是優(yōu)質品。

　　You get an A grade for scores of 75 and over.

　　75分及75以上的分數就是優(yōu)等。