“公然反对”可以用英语表达为 "openly oppose" 或 "publicly oppose"。
"openly oppose" 强调毫不掩饰、公开地表达反对意见。
"publicly oppose" 侧重于在公众场合或公开地表示反对。
例句：1、 They openly opposed the new policy during the meeting.（他们在会议上公然反对新政策。）
2、 The citizens publicly opposed the construction of the factory in their neighborhood.（市民们公开反对在附近建工厂。）