XMLHttpRequestObject = false;
	if(window.XMLHttpRequest){
			XMLHttpRequestObject = new XMLHttpRequest();
			//alert("Este browser es Firefox");
		} else if(window.ActiveXObject) {
			XMLHttpRequestObject= new ActiveXObject("Microsoft.XMLHTTP")
			}
			
			function getO3(marc,suby) {
					
				if(XMLHttpRequestObject) {
				XMLHttpRequestObject.open("GET","xmlModels.php?sub="+marc+"&suby="+suby);
				
					XMLHttpRequestObject.onreadystatechange = function () {
						if(XMLHttpRequestObject.readyState == 4 && XMLHttpRequestObject.status == 200 ) {
							var xmlDocument = XMLHttpRequestObject.responseXML;
							optionst = xmlDocument.getElementsByTagName("option");
						listOptions3();
						}
					}
					XMLHttpRequestObject.send(null);
				}
			}
			////////////// aqui enlisto la funcion de list options
			function listOptions3() {
			
			///// borra todos los registros del drop down
			for (i = document.getElementById('optionList3').length; i > 0; i--){
				document.getElementById('optionList3').options[i-1] = null
				}
				////////////////////////
				var loopIndex;
				var selectControl = document.getElementById('optionList3');
					for(loopIndex = 0; loopIndex < optionst.length;  loopIndex++) {
					selectControl.options[loopIndex] = new Option(optionst[loopIndex].firstChild.data);
					}
			}