These Dam Buttons

Hi,

Within a movie clip I have placed a series of buttons that when pressed produce a variable value.

I want the buttons when pressed (click) to keep its down state. At the moment when you move the mouse away from the button it just has the up or over state.

How do I keep the button in the down state once it has been clicked?

The idea is to show a ticket (for correctly answering a question) in a blank circle when the button is pressed down.

Any ideas?

Thanks

Dan