It is a very common thing for a person to have a good friend.My good friend is Diana.She is a rich and proud girl.She often thinks that she is too good for anyone,so nobody wants to be her friend. One day after school,I was waiting for Diana when Vivien came up to me.She gave me a biscuit.I accepted it.We talked and joked,and from then on,I began to spend more time with Vivien than with Diana.I felt a little uneasy. After a few days,I went to see Diana for some snacks when Vivien came and sat with me.She offered me a sandwich.She also offered one to Diana,but Diana refused it.She walked away.I was angry with Diana for being so rude and thoughtless. "Never mind,"Vivien said,"I'm used to it." After school,I tried to catch up with Diana.While walking home,I tried to correct her attitude,but she would not listen to me.She said,"Go and join your 'dear' Vivien.I know you make new friends and forget the old ones." For the next few weeks,we did not talk to each other.Then,one day,Diana came to Vivien and me,saying,"I'm really sorry about what I did.I'm a spoiled girl,but I also need good friends just like you.Would you please forgive me?"Vivien and I looked at each other and smiled.From then on,Diana,Vivien and I have been best friends." The reading is mainly about   _  .
the mistake among the three friends two best friends at a school three friends at a school the trouble between Diana and Vivien