"attachMoive" through a function

programming flash
1

Hey, im trying to attach a movie by calling it through a function, it doesnt like when I string the name within the function call and if I were to string it within the function it would look for that MC.

Heres the code of what I have


function addMovieMC(mcName:MovieClip) {
    _root.holder.attachMovie(mcName, btn, 1);
}
addMovieMC(btn1)