function ajaxFunction() {
  var xmlHttp;
  try {
    // Firefox, Opera 8.0+, Safari
    xmlHttp=new XMLHttpRequest();
  } catch (e){
		// Internet Explorer
		try{
		  xmlHttp=new ActiveXObject("Msxml2.XMLHTTP");
		} catch (e){
			try{
				xmlHttp=new ActiveXObject("Microsoft.XMLHTTP");
			} catch (e) {
				alert("Your browser does not support AJAX!");
				return false;
			}
		}
	}
	return xmlHttp;
}

var obj = ajaxFunction();

function getCarModelByMark(markid){
	ret = document.getElementById('car_models');
	obj = ajaxFunction();
	obj.onreadystatechange=function(){
		if(obj.readyState==4){
			ret.innerHTML = obj.responseText;
		}
	}
	obj.open("GET","_ajax_model_by_mark.php?id="+markid,true);
	obj.send(null);
}