【正确答案】正确答案：April 4th, 2015 Dear Zhang, Thanks so much for inviting us to join your son's birthday party in Hilton Hotel at 7 p.m. of April 20. I have seen the lovely baby before and it is worth celebrating for him and your happy family. But I regret that I cannot go to the party at that time. You know our company has a branch in Canada and it has something serious happened which needs my immediate decision. Thus I should go back as soon as possible. I am really sorry for my absence. Hope you will have a wonderful party and a good time. Sincerely, Tom Clancy

【答案解析】解析：此篇作文应为回复邀请的信函。在这类信函中要注意信的格式。写信时间应该写在右上角，称呼应顶格并首字母大写。正文要写清楚应邀还是拒绝，若拒绝，要写清楚理由，并向邀请人致歉。 第一段首先要对邀请表示感谢。 第二段表明自己去不了，并且明确告知具体原因。 第三段表达自己的歉意。