Answer: Functional distance
Explanation:
According to the given situation, the impact of the functional distance best illustrate about the friendship formation result.
The functional distance is basically refers to the physical distance between two people due to the architecture or the location according to the social psychologist.
The functional distance is basically defined as the arrangement of the residential facilities that influenced the social interaction and common mailboxes are one of the example of the physical distance.
Therefore, Functional distance is the correct answer.