The correct answer to this open question is the following.
Georg Simmel (1858-1918) is regarded as a micro sociologist because he developed the process of social development, intermixing the quantitative expansion of groups and social differentiation. He established that the smaller the group, the more vulnerable they were and that is why these groups had to ask their members more focus, effort, and involvement to be successful. On the other hand, the larger the group, the lesser involvement was needed because the members of these groups were diverse and segmented by affinities. In these groups, the relationships were impersonal and cold.
