Factors Influencing Interpersonal Attraction

In the realm of social psychology, interpersonal attraction plays a vital role in the formation of relationships. Factors influencing this attraction can include physical attractiveness, proximity, similarity, and others. A researcher is studying a group of college students and observes that those who often study together tend to develop closer relationships over time. Based on the principles of interpersonal attraction, which of the following factors is most likely influencing the bond between these students?