influence可數嗎

　　The media has a powerful influence on public opinion.

　　傳媒對于輿論有很大的影響。

　　No job has more influence on the future of the world.

　　沒有哪種工作對世界的未來具有更大的影響。

　　His family have been a very positive influence on him.

　　他的家庭對他有十分良好的影響。