✔ 最佳答案
Dear Principal,
I am sorry to inform you that I could not attend school from __(date)__th of June to __(date)__th of September. I have to go to China to figure out some important matters. I promise I will catch up with the teaching schedule and the working experience in July. I am really sorry for any inconvenience caused and I hope you will accept my leave.
Yours sincerely,
(your signature)
_(your name)__
Hope I can help you! There are probably some mistakes.. but at least it sounds a bit more polite:)) enjoy your studies!