Dr. Jones studies questions, such as why we conform to group norms, what compels us to obey authority figures, and under what conditions will people help a stranger. His research focuses on an area of social psychology called:

social influence.  

Explanation:

Social influence, in psychology, is referred to as the different ways in which a person changes his or her behavior in order to meet the demands of a specific 'social environment'. Social influence can take so many forms or types and therefore, it can be seen in various aspects including persuasion, peer pressure, conformity, obedience, sale, socialization, marketing, leadership, etc.

Types: Obedience, conformity, compliance.

As per the question, Dr Jones research focuses on an area of social psychology.

did mary wollstonecraft believe was a natural ingredient for women’s happiness?

so you should go with

a. strong

a is the final ! : )