级分的英文：
fraction
Centrifuging, washing, and filtering may separate any fraction of polymer that occurred by an emulsion process
离心，洗涤，和过滤可以分离乳液法制得的任何级分的聚合物。
n. 小部分，少量，一点儿；分数，小数
Could you move a fraction closer?
你能不能稍微再挪近点儿？
In this case the fractional part is discarded.
在此情况下小数部分被丢掉了。
You do fractions, then you do decimals.
你先学习分数，然后，学习小数。
One forth is a proper fraction.
四分之一是一个真分数。
Fraction is really complicated.
分数真是复杂。