Dear Mr Chen,
I'm sorry to tell you that I can't go to school today.I've caught a coldbecause I swam in the Kunming Lake yesterday.
This morning I had a headache.After taking my temperature,my mother foundthat I had a high fever.She took me to see a doctor.The doctor advised me tostay in bed for two days.
Now I'm writing to you to ask for two days' sick leave.
Yours respectfully
Dear mr.li,