Final answer:
The Russian enthusiasts' group had influence over just a small part of the members' behavior, focused on their interest in Russian language and culture.
Step-by-step explanation:
Marion belonged to a group that got together once a month in group members' houses to converse in Russian, which they had all learned in school. The Russian enthusiasts were an example of a group that wielded influence over just a small part of their behavior. This is because their group activities are limited to practicing the Russian language and culture, which constitutes only a segment of their overall daily lives and behaviors, rather than influencing vast segments of behavior or many aspects of life as broader social institutions might.