title: Preventing user from uncheking a checkbox
body: <p>I have 3 checkboxes in my winforms program. I managed to make it somehow that only one of them can be selected by user. That is if user clicks one of the unchecked buttons, ofcourse that button will be checked and also the check will be removed from last checked button!</p>
  
  <p>Now I want to do it somehow that user can not uncheck the checkboxes, so the only way to checkk a box will be clicking on it. is this possible? is there any property for this?</p>
  
  <p>Sorry for using too much check &amp; box :P</p>