Dear Ms Lewis,
(before opening) I hope this letter finds you well.
(opening 1 introduction) I'm Li Hua, one of your students in Class One Senior Three. (opening 2 intention) I'm writing with regret to request permission for sick leave tomorrow morning due to the medical appointment.
(body 1 reason for leave) I don't feel well after lunch today, for which I've got to go for a body check scheduled at 10 the next day. However, I shall be back on 12th March. (body 2 demand for help) Besides, I'm wondering if you're so kind to offer me your assistance on the missed work later.
(closing 1 apology and acknowledgement) I apologize for any inconvenience caused but appreciate in advance your help. (closing 2 expectation) Please keep me informed about the time.
Yours,
Li Hua