Prob with horizontal menu

Hi,

I am creating an horizontal menu.Where if an item selected it gets an arrow on the top to show its selected.My prob is if i clicked all the items all of them are having an arrow at the same time.Actually one arrow should move to the selected menu item .
How can I do that?
I put the function which create arrow in the onRelease event of the items.Items being M.C ofcourse.