I would like some help with the following expressions, as I see them used in different ways:
Actions to reduce pollution at a/the municipal level play a crucial role.
Actions to reduce pollution at municipal level play a crucial role.
Actions to reduce pollution at a/the international level play a crucial role.
Actions to reduce pollution at international level play a crucial role.
Actions to reduce pollution at a/the local level play a crucial role.
Actions to reduce pollution at local level play a crucial role.
Actions to reduce pollution at a/the sector level play a crucial role.
Actions to reduce pollution at sector level play a crucial role.
My question is about using the article "a/the" or not when it comes to sentences of this kind, is there a rule or it depends on the word preceding "level"?
If yes which one (a or the)?
Thank you