Dear Mr/Ms Zhang,
I would like to apply for a sick leave from the 8th to 10th of April as I had an accident yesterday. On my way home from school, I fell from my bicycle. Thankfully a kind person sent me to the hospital in time. My doctor advised three days of bed rest, and I will not be able to come to school during this time. I'm sorry for any inconvenience caused.
Regards,
Zhang Lin