Social networks are a natural tool for bringing together ________,people who engage in similar work,and ________,people who share enthusiasm for a particular product or activity.

A) private networks; public networks
B) virtual networks; brand societies
C) communities of practice; communities of interest
D) special interest groups; word-of-mouth conclaves

Communities of practice refer to groups of people who share a profession or engage in similar work, while communities of interest refer to groups of people who share a common interest or hobby. These two types of communities are well-suited for social networks, making choice C the correct answer. Private and public networks, virtual networks and brand societies, special interest groups, and word-of-mouth conclaves are not as specific as communities of practice and interest, and therefore not the best choice(s) for completing the sentence.