<!--

  //Precarga
  if (document.images) {
    // opcion 1
    var but1 = new Image();
    but1.src = "img/but1.gif";
    var butov= new Image();
    butov.src = "img/butov.gif";

    // opcion 2
    var but2 = new Image();
    but2.src = "img/but2.gif";
    // opcion 3
    var but3 = new Image();
    but3.src = "img/but3.gif";
    // opcion 4
    var but4 = new Image();
    but4.src = "img/but4.gif";
    // opcion 5
    var but5 = new Image();
    but5.src = "img/but5.gif";
    // opcion 6
    var but6 = new Image();
    but6.src = "img/but6.gif";

    // otras opciones
    var tmback = new Image();
    tmback.src = "img/tmback.gif";
    var tmbacksel= new Image();
    tmbacksel.src = "img/tmbacksel.gif";

  }
  
  // Para el regreso (boton de teacher manual)
  function tmrollOver(over) {
    if (!document.images) {return};
    whichIm = document.images["tmback"];
    if (over) { 
      whichIm.src = "img/tmbacksel.gif" }
    else { 
      whichIm.src = "img/tmback.gif" }
  }
 
  function rollOver(imName,over) {
    if (!document.images) {return};
    whichIm = document.images[imName];
    if (over) { 
      whichIm.src = "img/butov.gif" }
    else { 
      whichIm.src = "img/" + imName + ".gif" }
  }
// -->