题目内容：

The policeman wouldn't have believed me if you hadn't back me up
wouldn't have believed me 不要只翻译,还要语法解释,因为我这个语法点不明,

优质解答

sb wouldn't have done sth 本不会做某事,意味者某人本不会做这件事.wouldn't have believed me本不会相信我.