It's about ___the thickness of a human hair

12. It's about__ , the thickness of a human hair.

A. two-fifteenth B. two-fifteenths C. two fifteen D. two fifteens

12.答案為B。

分數做定語，分子用基數詞，分母為序數詞，當分子大於1時，分母用復數，

本題中，其它表達方式均不正確。