Which of the Following Was Demonstrated by Melvin Kohn's Research

Which of the following was demonstrated by Melvin Kohn's research on "occupational self-direction?"

A) Workers in more complex jobs become less fatalistic and more self-confident.
B) People with few things that interest them are more likely to choose jobs that require little thinking.
C) Many people become self-employed because they don't like taking directions from other people.
D) People working alone are generally more satisfied than those who work in groups.