Help with random

i’m using Mx Flash and i am making a game. it is called “falldown”. the ‘ledges’ that you run into as you are falling down need to go up. i have the mc that moves up and all, but there needs to be three of them that move up to keep you from hitting the bottom. i need it to randomly pick from the three mcs as the first one reaches a certain point. in case you don’t understand ask questions and i am going to post the .fla when i get on my own comp.