【正确答案】 C

【答案解析】细节题。本题答案在第三段“If productivity is the primary determinant of living standards，other explanations must be of secondary importance．For example，people might think that labor unions or minimum-wage laws contributed to the rise in living standards of American workers over the past century．Yet the real hero of American workers is their rising productivity．”由上面的论述可知，生产力对人们的生活水平起决定作用，其他因素都是次要的。