I'm sorry,_____________I can't go to the movies with you 横上上的词用and还是but?

but but 用于表示歉意的话语后,引起一个分句,but本身无意义.如：I’m sorry,but I think you are wrong when you say she did it willingly.抱歉,你说她情愿做那件事,我觉得你搞错了.Excuse me,but are you Mr.Smith...