window.onload = function () {
  document.getElementById("submit_categoria").style.display = "none";
  document.getElementById("submit_autor").style.display = "none";
  document.getElementById("submit_editorial").style.display = "none";
  document.getElementById("select_categoria").onchange = function () { document.forms[1].submit(); }
  document.getElementById("select_autor").onchange = function () { document.forms[2].submit(); }
  document.getElementById("select_editorial").onchange = function () { document.forms[3].submit(); }
}