function setWards(o) {
    $.getJSON('/Home/GetWards/?cbd_id=' + o.value, null, function(data) {
        $('#ward').empty();
        $.each(data, function(i, item) {                   
            $('<option/>').attr('value', item.ID).html(item.Name).appendTo('#ward');
        });
    });
}
 
public JsonResult GetWards(int cbd_id)
{
    return (this.Json((from w in db.Wards
                       where w.CBUID == cbd_id
                       select new
                       {
                           ID = w.ID,
                           Name = w.Name
                       }
                       ).ToList()));          
                         
}
 
<%= Html.DropDownList("ward", Model.Wards, new { @class = "sectionDD" })  %>