问通过ajax将多个值发送到另一个页面

EN

  function rates()
        {
       var a=document.getElementById("measure_unit").value; 

b=document.getElementById("weight_slot").value;



 if (a=="")
        {
      document.getElementById("credit7").innerHTML="";

      return;
}


          if (window.XMLHttpRequest)
          {// code for IE7+, Firefox, Chrome, Opera, Safari
         xmlhttp=new XMLHttpRequest();
        }
         else
          {// code for IE6, IE5
         xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
          }
      xmlhttp.onreadystatechange=function()
           {
       if (xmlhttp.readyState==4 && xmlhttp.status==200)
{
//document.getElementById("ajax_details2").innerHTML=xmlhttp.responseText;
    document.getElementById("credit7").innerHTML=xmlhttp.responseText;

}
     }
        xmlhttp.open("GET","ajax/rate_details.php?q="+a,true);

    xmlhttp.send();     


 }

            <?php
          include 'dbcon.php';
         $q = $_GET['q'];