One possible version:
Dear Tim,
How are you doing recently?
I'm writing to invite you to join us in a summer camp. Our school plans to have a four-week summer camp, from July 15 to August 12. There'll be both Chinese and international students. In the mornings, we'll have classes including Chinese, English and Chinese painting. In the afternoons, there'll be lectures on Chinese culture and customs. On weekends, we'll tour around the city and visit some places of interest, such as the Great Wall and the Summer Palace. We are sure to have a lot of fun together. So what do you think of it?
I'm looking forward to your early reply.
该篇作文属于应用文文体写作，要求写信人给Tim写信介绍自己学校的夏令营并且邀请他参加。在写作时，考生首先应该注意电子邮件的基本格式；其次，注意写信人与收信人之间的关系（即朋友关系）；最后，还要注意正文部分的写作层次。根据题目要求，正文部分应按照层次来写，即介绍时间、具体内容，最后邀请他来参加。同时，还要注意最后的写信人的姓名要用“Li Hua"代替，而不能写成自己的名字或者其他的名字。
【高频词汇】
How are you doing recently? 你最近过得怎么样？常用于书信的开头表示问候。
plan to do：计划做某事
I'm looking forward to your reply：期待你的回信
