4.a) I guess the main reason why XXX and I became best friends, is that we have the same interests.
b) For example, we both love listening to music, and we spend many hours together listening to our favorite CD`s.
5.a) Another reason why we have become best friends is that we both would like to go and study abroad in the near future.
b) So we often chat about what possible majors we would study, and what university we would like to attend.
6.a) A third reason why s/he is my best friend is that we share many principles.
b) For example, we both believe that we should not damage our health by smoking cigarettes.
7.a) Lastly, I believe that XXX has had a positive influence on my life since we have met.
b) XXX is always friendly, cares about his/her family and friends, and is always willing to listen to others.
So now you know why XXX is my best friend.
