Dear Mrs.Miller,
I'm so sorry I can't go to school for a couple of days. I've had a running nose and a bad cough for the last three days. I had a fever yesterday and I have been feeling strengthless ever since. I went to the hospital this morning to check what's going on, and the docter told me that I had flu and that I should stay in bed for the next 2 to 3 days. So I am asking for leave for 2 days. If you give me permission to stay home, I will really appreciate it. Also, could you please ask my classmates to pay extra attention to their health, in case they caught my flu. I am really sorry for the inconveniences I caused. Hope everything is OK. Best wishes.
Yours sincerely,
Li Jing
Date:XXXXXXXXXX
（你给出的要求都达到了,格式和礼貌用语也应该没有问题.我给你加了一句话,就是叫同学们注意身体健康,是因为我觉得流感这东东会传染的啊,应该提一下~希望对你有帮助O(∩_∩)O）