lifestyles, have found that having good friends can help you live longer. An American study of 10,000 students, over a period of 35 years, also found that if you make more friends than the average (普通的) person at school, you'll receive a higher salary (工资) in later life. People need good social skills at work to manage people and work in a team successfully. These are the same skills we use to make friends at school.

　　On average, teenagers aged between 15 and 17 have 500 "friends" on their favourite social networking site. Adults (成年人) have 130. So if you believe this research, you might live for a long time and be very rich.

　　However, according to Professor Robin Dunbar from the University of Oxford, it probably won't make any difference. Dunbar studied the number of messages between users of a popular social networking website, each of whom had between 200 and 2,000 friends. He found that they always communicate with a maximum (最大量) of 150 people.

　　Among these 150, Dunbar believes that around five people are close friends. You've most likely known them for a long time; they are probably old friends and you share all your good and bad experiences with them. Then there are ten more friends. Although they're close to you, you may not keep in touch with them every week. Next there are 35 people who you might spend time with because of a shared interest. You aren't close. And finally, there's a large group of 100. You see or speak to these people at least once a year, but you don't know them well. Beyond (超过) this_number,_Dunbar says, it's impossible to make any relationship meaningful.

If you have a lot of online "friends"， try this experiment: First take away anyone you haven't been in touch with for a year. Then remove people you can't remember and, finally, take away friends who you wouldn't mind losing touch with. How many do you have left? How many of these people are actually good friends? According to the research, these are the only peopl