How to limit the number of options in the drop-down in front-end which is based on the value that is chosen by the admin in back-end for a drop-down which having options as 'single' and 'Multiple'. When admin choose option 'Single' and save a product from back-end , only one drop-down value is there in front-end for a custom drop-down. How to do that? Any idea? Any link for referal ?