The answer is "a. social psychology".
Social psychology is the logical study of how individuals' thoughts, emotions, and practices are impacted by the real, envisioned, or inferred nearness of others.
The terms thoughts, emotions, and practices incorporate the majority of the mental factors that are quantifiable in a person.
The reference to envisioned or inferred others recommends that we are inclined to social impact notwithstanding when no other individuals are available, for example, when sitting in front of the TV, or following internalized social standards.