DearMr/Mrs/MsXXX(teacher):
Iamwritingthislettertoaskforyourpardonformyabsenceinyourclass.
AsCET-6isaroundthecorner,IrealizedhowmuchIamlaggedbehindformypreparationschedule.TheonlychoiceIhaveistoborrowsometimefrommyclassesforthisupcomingexamwhichissoimportantforme.IamterriblysorrythatIcannotmaketoyourclass,andIwouldbegratefulforyourunderstanding.
ThankyouforyourunderstandingandIdoappreciateirverymuch.IwillmakeeveryeffortinmakingupwhatImaymissfromyourlesson.
Yours
XXX