听力原文：Many interesting sites have come up on the Internet in recent years, but one of the most successful sites has been "oldfriends. com". Like all good ideas, this one is very simple. It's just a database of schools that you can add your name and e-mail address or phone number to, so that old friends can log on, find your details and contact you. In the studio today, we have two guests Mark Sorenson, a sociologist who has been investigating this phenomenon and Dr. Julie Arnforth, a psychologist who has recently produced a study of how and why friendships from the past can become very important to us in later life.
Who is speaking？

A sociologist
B. An old friend
C. Dr. Julie Arnforth
D. A radio or TV presenter