案例分析题Americans use the word" friend" in their own way. Americans have school friends, work friends, and sports friends. These friendships grow out of the same interests. When people no longer do the same thing out of the same interests, the friendship may end.In some cultures(文化) friendship between two people may last for a lifetime. In these cultures friendships develop slowly, since they are built to last. American society (社会) is one of fast change. Studies show that one out of five American families move every year. American friendships develop quickly, and they may change just as quickly. Americans may seem very friendly and they often talk easily with strangers. They give each other information about their families, hobbies and work. They may smile warmly and say "Have a nice day" or "See you later". Students may say to each other, "Let’s get together sometime." But American friendliness does not always mean true friendship.Outsiders may think that Americans are too changeable, but learning what Americans think of friendship can help non-Americans keep away from misunderstandings (误解). It can also help them make friends the American way. Why do American friendships develop and change quickly（）

A. Because American society changes quickly.
Because Americans like to talk with strangers.
C. Because Americans often change their hobbies.