2. Wikipedia says: A social network is a social structuremadeup of individuals (or organizations) called "nodes", which are tied (connected) by one or more specific types of interdependacy, such as firendshipkindship, common interest, financial exchange, dislike, sexual things, or relationships of beliefs, knowledge or prestige.
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4. Facebook & Twitter This two are the 2 websites most visited by people in America in social networking.