A close friend is someone who you get on really well with,who helps you when you have problems,who gives you advice,and who always has time for you.They probably have similar hobbies to you so you can do things together. Researchers in Australia,who studied 1,500 people and their lifestyles,have found that having close friends can help you live longer.An American study also found that if you make more friends at school,you’ll receive a higher salary①in later life. On average,teenagers have 500 “friends”.Adults② have 130.So if you believe this research,you might live for a long time and be very rich.However,according to a professor from Oxford University,it probably won’t make any difference.He found that they always communicate with a maximum③of 150 people.