influence可数吗

　　The media has a powerful influence on public opinion.

　　传媒对于舆论有很大的影响。

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

　　没有哪种工作对世界的未来具有更大的影响。

　　His family have been a very positive influence on him.

　　他的家庭对他有十分良好的影响。