婉谢邀请信函
dear sirs，
my wife and i were very grateful to receive an invitation to attend the celebrations marking the opening of your new factory．we are sorry to inform you that we have to decline your invitation owing to a previous engagement．
yours faithfully，
中文对照
敬启者：
我和夫人非常感谢阁下邀请参加贵公司新建工厂开业典礼庆祝仪式。但由于事先有约，无法应邀前来参加，深表遗憾。
敬上