【正确答案】Dear Tom,
I am terribly sorry to tell you that I am unable to attend your weeding ceremony next Thursday evening.
That is owing to the fact that my younger brother suddenly fell ill and was taken to a hospital this around five days for him to recover and take care of him．As told by the doctor in charge, it will take around five days for him to recover and I have asked my boss for a leave.
I really regret that I cannot go to celebrate your wedding personally. I have chosen a small gift for you and will send it by post to show my best wishes.

【答案解析】从所给的信息可以判断，本题要求完成的是一封道歉信。道歉信可以分为私人道歉信和正式道歉信两种。通常，私人的道歉信用词要坦率和诚恳；而正式道歉信则要用词严谨，可使用套话。本题属于私人道歉信，一般包含三个方面的内容：点明道歉的事情，并表示诚恳的歉意；简明扼要解释事情发生的原因；再次表示遗憾和歉意，并提出补救措施。