Multiple drag and drop

1

I am doing an interactive exercise with drag and drop function. The problem is when user drag movie clip" A" on to targeted area “B”, but later when he changes his mind and drag movie clip 'C" onto “B”, “C” will overlap “A”.How can i make “A” goes back to it’s orignal position? I have 9 draggable clip and 9 targeted areas. Thanks for the help!