【正确答案】
[范文]
Dear David,
I am afraid that you will think me unpardonably negligent in not having answered your letter dated 7th, June 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.
Sincerely yours,
U Ming

【答案解析】[审题]
这是一封道歉信，是写信人对未尽之事表示歉意。一定要注意语言的诚挚与理由的真实。写作方法：1)首段：对未尽之事表示歉意；2)主体：详细解释事由，目的是消除可能产生的误会和矛盾；3)尾段：再次表示歉意，表明愿意补救或提出其他建议。