Set/reset drop down list item

Set/reset drop down list item

I've created a drop down list as below:
<select name="declinereasons" id="declinereasons" onchange="declinereasonsChanged();" >
                </select>

And on some event I call the following function to fill my drop down


function fillDeclineReasonList() {
        $.getJSON('<%= ResolveUrl("~/myurl/")%>', function (data) {
            ReasonCollections = data;
            var items = "";
            items += "<option value=''>Select One</option>";
            $.each(data, function (i, ReasonCollections) {
                items += "<option value='" + ReasonCollections.Value + "'>" + ReasonCollections.Text + "</option>";
            });
            items += "<option value='Others'>Others</option>";
            $("#declinereasons").html(items);
        });
    }

But on certain event I want to set one of the value from this list to be selected and also to make reset the value on clicking on the reset button please help me how I can perform these needed oprations.