dearsirs，mywifeandiwereverygratefuoreceiveaninvitationtoattendthecelebrationsmarkinheopeningofyournewfactory.wearesorrytoinformyouthatwehavetodeclineyourinvitationowinoapreviousengagement.yoursfaithfully，中文敬启者：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...