写英语邀请信,邀请外教参加班级的野炊活动?

Dear Sir/ Madam/ Mr.XX/Ms.XX
I'm your student,xxx,and I want to invite you to join the picnic hold by my class.
The picnic will take place from 起始日期 to 终止日期,and the main purpose is to strengthen our friendship and understanding.
We also prepare several activities such as xxx.
If you have spare time at that time,we hope you can join us.
Yours faithfully
xxx
主要要把你的身份,参加的活动,活动时间写清楚.