<script type="text/javascript">
    var txtcity= '<%= txt_city.ClientID %>';
        var txtkeys = '<%= txt_key.ClientID %>';
        var txtarea = '<%= txt_area.ClientID %>';
        var auto2='<%= AutoCompleteExtender2.ClientID %>';
        var auto3='<%= AutoCompleteExtender3.ClientID %>';
        var controls = {
              "txt_city": txtcity,
              "txt_key": txtkeys,
               "txt_area": txtarea,
                "AutoCompleteExtender2":auto2,
                    "AutoCompleteExtender3":auto3

};

        function IAmSelected(source, eventArgs) {
             $find(auto2).set_contextKey(eventArgs.get_value());
            $find(auto3).set_contextKey(eventArgs.get_value());
       }
        
       
                    
       
        </script>