［参考范文］
Dear Sir,

　　Please excuse my absence from class today, because I got a bad cold yesterday evening and didn't well in the night. I felt even worse this morning. Therefore, I had to go to the doctor to have myself thoroughtly examined. Thus, I am writing to ask you for a day's sick leave and assure that I'll resume my study if I feel any better tomorrow.

　　　　　　　　　　　　　　　　　　　　　　　Sincerely
　　　　　　　　　　　　　　　　　　　　　　　Li Mingming