答案：Dear Mr Black,
I'm Peter, a Grade 7 student in our school. I'm 13 years old, and I love doing all kinds of sports in my free time.
My favourite sport is football. I often play it with my friends after school, because it makes me strong and happy, and I really enjoy playing with teammates. My dream is to be a good football player. I really hope I can join our school football team.
I'm looking forward to your reply.
Yours,
Peter