Final answer:
Primary relationships are more likely to develop in small groups where it's easier to know each other well, facilitated by regular contact and a sense of connection.
Step-by-step explanation:
Primary relationships are more likely to develop if the size of the group is small because it is easier to know each other well in this setting. In a small group, people can engage in more meaningful interactions and build closer ties, as opposed to larger groups where individual relationships may be more superficial. Proximity is key to forming relationships, as regular contact with others increases the likelihood of a bond forming. This explains why relationships such as friendships or romantic partnerships often originate from those we see frequently, like neighbors or classmates. Additionally, small groups provide a sense of cohesiveness and connection, which can foster the development of primary relationships so long as all members know each other and share simultaneous interaction.