What Do Sociologists Mean When They Say That Education Serves

What do sociologists mean when they say that education serves a credentialing function?

A) that schools seek to maximize educational outcomes of students
B) that education doesn't change people but moves them along different routes that influence how much they earn
C) that education limits entry into some occupations and thus raises the rewards for people in them
D) that schools with the best-performing teachers produce more students who earn multiple degrees