【正确答案】[范文]
   
Dear Sir,
   I'm John Green from after-sale department, Leek Air-conditioning Company. I'm writing to express my deep apology for the neglect of my job.
   I received your letter yesterday, which said that your newly bought air conditioner was not fixed as scheduled. I am terribly sorry for that. All of this is due to the fact that I misread the time. And we promise to finish the installment next Monday.
   I sincerely apologize to you for the inconvenience caused by my mistake again.