Our birth families (mother, father, sister, and so on) are a central part of our lives. Suppose you family decides to host a foreign exchange student for a year. It goes well, and, the next year, the student's entire family (all nine of them) decides to visit America and your family. In the ensuing year, various members of the two families stay in touch, and you share these relationships with your own friends. In the context of social networks, what's happening between your two families, as well as the way you share the experience with your friends, is what sociologists call a tie, and although the two families are unrelated, this "tie that binds" is made real because of _________