Dear Mr/Ms XXX;

　　Today I'm writing to you to ask for a five-day leave, for I've got cold last night with carlessness.

　　This morning my mother took me to see the doctor,who told me to stay in bed for some days. So I am very sorry to be absent from school, especially your interesting lessons. I'll be sure to make up for the missed lessons after I recover from the illness.

　　Yours ever,

　　XXX.