MC depths

hello,

i need help with finding out which mc is underneath the current one.
here is my code to attach movies, buttons “b1 through b5”, and “words1 through words5” is the content. getting attached in “holder” on _root.

 
for (var i = 1; i<6; i++) {
_root.nav["b"+i].onPress = function() {
num = this._name.toString().substring(1, 2);
_root.holder.attachMovie("words"+num, "words"+num, _root.holder.getNextHighestDepth());
};
}

once it is attached how could i get the mc on the depth below it?

thanks for help anyone.