因迟复来信致歉Because of answering one’s letter late

Dear David:

I am afraid that you will think me unpardonably negligent in not having answered your letter dated7, December sooner, but when I have told you the reason, I trust you will be convinced that the neglect was excusable. When your letter arrived, I was just in Hong Kong. As my family could not forward it to me during my absence, it has been, therefore, lying on my desk until the moment when I took it up. Now the first thing I have to hasten to do is to write to you these few lines to express my deep regret. 

I enjoyed many pleasant sights during my trip. I shall be pleased to give you an account to of them when I see you next. 

Sincerely yours, 

Tom