Passing Variables betwen Functions

I am attempting to create a simple conditional animation but I’m having problems passing the conditions around.

I have three separate movieclips: (A, B, C) that can all be triggered by user actions.

If any one of the three clips is currently playing, none of the other clips should play.

If a movieclip is triggered by a user action, I need to check if any of the clips are still playing before it can play the clip.

Initially I set up a series of if/then statements in the mouse_click functions dependant upon a variable being passed between all the separate functions. The functions could not accept both a mouse click, and a variable.

Why not? How can I get around this?

Is there a better to way to accomplish what I am attempting?

Thanks in advance!!