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 is not uncommon for Americans to have only one close friend during their lifetime, and consider other 'friends' to be just social acquaintances. This attitude probably has something to do with American mobility and the fact that Americans do not like to be dependent on other people. They tend to 'compartmentalize' (划分) friendships, having 'friends at work', 'friends on the softball team', 'family friends', etc.. 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 charged atmosphere, Americans can sometimes seem brusque (无礼的) or impatient. They want to get to know you as quickly as possible and then move on to something else. Sometimes, early on, they will ask you questions that you may feel are very personal. No insult is intended the questions usually grow out of their genuine 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 behavior. 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 in fact that you may become tired of listening. It doesn't matter because Americans tend to be uncomfortable with silence during a conversation. They would rather talk about the weather or the latest sports scores, for example, than deal with silence. On the other hand, don't 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. The general topic of the passage is______.