回答如下:

Dear Miss Evans,

How are you doing?

I am very sorry about being absent from my today's classes because of my illness.This morning I had a stomachache and I felt so terrible. Then my mother took me to see a doctor. The doctor asked me to stay at home and have a good rest for two days. It is our fault that we didn't ring you up in time to ask for two day's leave. Now I am feeling much better after taking some medicine. I am going back to school the day after tomorrow.

Last, please allow me to apologize to you again for my forgetting to ask for leave in time.

Good luck!

Your sincerely,

Jack