function loadModelsESize(make_id){
   clearSelectList(document.TopNav.model_combo);
   clearSelectList(document.TopNav.esize_combo);
   if (make_id){
// model processing
       eval('var model_list = Models'+make_id+'();');
       for (var i = 0; i < model_list.length; i++) {
               document.TopNav.model_combo.options[i+1] = model_list[i];
       }
//       document.TopNav.model_combo.disabled = document.TopNav.model_combo.options.length==0;
// engine size processing
       eval('var esize_list = EngineSizes'+make_id+'();');
       for (var i = 0; i < esize_list.length; i++) {
               document.TopNav.esize_combo.options[i+1] = esize_list[i];
       }
//       document.TopNav.esize_combo.disabled = document.TopNav.esize_combo.options.length==0;
       }
  }


function clearSelectList(selList) {
   for (var i = 0; i < (selList.options.length-1); i++) {
             selList.options[i+1]=null;
   }
   selList.options.length = 1;
//   selList.disabled = true;
}

function checkRequiredFields(){
  ok = true;
  if (document.TopNav.make_combo.options.selectedIndex==0){
    ok = false;
  }

  if (ok && document.TopNav.model_combo.options.selectedIndex==0){
    ok = false;
  }

  if (ok && document.TopNav.esize_combo.options.selectedIndex==0){
    ok = false;
  }

  if (ok && document.TopNav.year_combo.options.selectedIndex==0){
    ok = false;
  }

  if (!ok) alert ("Please, fill all select criteria");
  return ok;
}