DearAnne,
Thankyouforyourinvitationtodinneratyourhometomorrowevening.
Unfortunately,itismuchtomyregretthatIcannotjoinyouandyourfamily,becauseIwillbefullyoccupiedthenforanimportantexamcomingthedayaftertomorrow.Ifeelterriblysorryformissingthechanceofsuchahappyget-together,andIhopethatallofyouenjoyagoodtime.Isitpossibleforyouandmetohaveaprivatemeetingafterward?
Ifso,pleasedon'thesitatetodropmealineaboutyourpreferabledate.Idolongforapleasantchatwithyou.
Pleaseallowmetosaysorryagain.
Regards,
LiMing