A、American society. B、American culture. C、Americans’ personality. D、Americans’ activity. CWhat is the main topic of this passage

Americans usually consider themselves a friendly people. Their friendships, however, tend to be shorter and more casual than friendships among people from other cultures. It’s not uncommon for Americans to have only one close friend during their lifetime. They tend to divide friendships, having "friends at work", "friends on the softball team", "family friends" and so on.  Because the United States is a highly active society, full of movement and change, people always seem to be on the go. In this highly changed atmosphere, Americans can sometimes seem impolite or impatient. They want to get to know you as quickly as possible and then move on to something else. Sometimes, at first, they will ask you questions that you feel very personal.  No result is intended; the questions usually grow out of their real interest or curiosity, and their impatience to get to the heart of the matter. And the same goes for you. If you do not understand certain American behaviors or you want to know more about them, do not hesitate to ask them questions about themselves. Americans are usually eager to explain all about their country or anything "American’ in which you may be interested. So much so that you may become tired of listening. It doesn’t matter, because Americans tend to be uncomfortable with silence during conversation. They would rather talk about the weather or the latest sports scores that deal with silence. On the other hand, do not expect Americans to be knowledgeable about international geography or world affairs, unless those subjects directly involve the United States.  Because the United States is not surrounded by many other nations, some Americans tend to ignore the rest of the world.