AS3 Help for Flash Drag and Drop Game

The user has to select the correct answer and drag and drop it to the correct position based on the hint provided in the game. Altogether there will be five options for the user to select. The drag and drop works fine with the code. I want to restrict the user from selecting multiple options? What i really need to do is once a option is selected by the user it should prompt whether the selected answer is accurate or not. Can anyone help me with this?

Thanks