Say I got 4 dropdownlists to which I load/clear data as the one of them change:

Countries
Regions
Cities
Suburbs.

When the form load, only Countries are populate with data, the rest are hidden. (ok)
When Countries change, Regions are shown, data are loaded.
And so on.
When all are populated, and say Countries change, Regions are loaded with data, Cities and Suburbs cleared and hidden.
(I think you get the picture).

Following is what I got now, but it comes down to be able to determine the next dropdownlist of "this" and the one's following that (the first to be loaded with data, the rest to be cleared/hidden).
I only pasted the first one. The rest (one for region change, one for city change are the same, just with less being cleared and hidden.)
Note this works fine. I just want some expert advice on how to refactor it into something .... simpler / less code / less duplication)

Code:
   <script type="text/javascript">
        $(function () {

            // hide all empty dropdowns when the form load
            // TODO: how to select dropdowns that are empty?
            $("select#RegionId").hide();
            $("select#CityId").hide();
            $("select#SuburbId").hide();

            $("select#CountryId").change(function () {
                
                // clear and hide dropdowns that will not be used now
                // TODO: there's a way to modify the selection after remove and call hide...no?
                $("select#CityId>option").remove();
                $("select#CityId").hide();
                $("select#SuburbId>option").remove().hide();
                $("select#SuburbId").hide();
                
                // also hide the region list while getting the data
                $("select#RegionId>option").remove();
                $("select#RegionId").hide();
                
                var countryId = $(this).val();
                var urlAction = "/Shared/CountryRegionsSelectList/" + countryId;
                $.getJSON(urlAction, { countryId: countryId }, function (data) {
                    $("#RegionId").addItems(data.d).show();
                });                
            });
      ...............  rest are similiar