GTM - Track Drop-down selection

<script>
  (function() {
    // Adjusted the CSS selector to suit your website
    var menus = document.querySelectorAll('select#region,select#funcion,select#tecnologia');

    var callback = function(e) {
      var selectedOption = e.target.options[e.target.selectedIndex];
      window.dataLayer.push({
        event: 'selectionMade',
        selectedElement: selectedOption
      });
    };

    menus.forEach(function(menu) {
    menu.addEventListener('change', callback, true);
    })();
  })();
</script>