happen to do sth和happen doing sth区别如下： happen to do sth 译为碰巧、正好做了某事.（一般现在时）例如：别人问你借钱,你 …
happen to do sth.是固定词组，“碰巧做某事”的意思 I happened to sit by her in the cinema.在电影院我碰巧坐在她旁边。 …