Hi Nicole - thanks for your question!

You have a really good rationale for why you chose the answer you did and it sounds like a good understanding of what an agent of socialization is. To re-define an agent of socialization, this term refers to people, organizations and institutions that help us learn about our social world and impress social norms upon us. Agents of socialization help us to use the objects of our society’s material culture, and adopt the beliefs, values, and norms that represent nonmaterial culture.

This learning takes place through interaction with various agents of socialization, like peer groups and families, plus both formal and informal social institutions. The most commonly cited agents of socialization include social groups (family and peers) and institutional agents including schools, workplaces, religion and the government as well as mass media.

While agents of socialization definitely differ across geographical locations and eras, the MCAT is testing understanding on the most common and important influences on socialization. It can be true that for those who don't interact with mass media or religious institutions, these will play less important roles in the process of socialization. However, on a global scale these are more likely to influence our understanding of the world around us than direct/indirect contact with an influential philosopher.

Hope this helps!
-Sydney