答案是B
two-thirds
About two-thirds of of the workers in this car factory were born in the 1970s
这个汽车厂工人中三分之二是70后的.
表示分数的要用s,用不用连字符请看
分数当修饰语时要用连字号；分数当名词时,可用连字号,也可不用连字号.
We were short of a two-thirds majority.
Two-thirds of the apples were bad.
Two thirds of the work is finished.