Dear MR. Johnson,
I'm writing to ask for leave from your oral English class this Wednesday morning.
Yesterday i got a phone call from my uncle.He needs an interpreter for one day.His business partner from Britain has come.He knows that my oral English is good so that he wants me to have a try.I think it is a good opportunity to put what i have learned in your class into practice,but ineed your permission of absence first.If you allow me to go and help him,I am confident that i'll do a good job and both of us will be greatful.
Looking forward to your reply.
Yours,
Li Hua