How to receive data from server page in ajax?

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ASP.NET

Javascript

Ajax

I am a beginner in ajax asp.net.
When i want to back data from server page to client page after ajax request, i do not know how to send back data to client.

string te = "hello world";
System.Text.StringBuilder sb = new System.Text.StringBuilder("<?xml version=\"1.0\"?>");
        sb.Append("<Employee>");
        sb.Append("<EmployeeID><![CDATA[" + te + "]]></EmployeeID>");
        sb.Append("<FirstName><![CDATA[" + te + "]]></FirstName>");
        sb.Append("<LastName><![CDATA[" + te + "]]></LastName>");
        sb.Append("<Phone><![CDATA[" + te + "]]></Phone>");
        sb.Append("<Title><![CDATA[" + te + "]]></Title>");
        sb.Append("<BirthDate><![CDATA[" + te + "]]></BirthDate>");
        sb.Append("<HireDate><![CDATA[" + te + "]]></HireDate>");
        sb.Append("</Employee>");        
        Response.ContentType = "text/xml";
        Response.CacheControl = "no-cache";
        Response.Write(sb.ToString());

And in client page i receive it in this way:

if(XMLHTTP.status == 200) {        
	var x=XMLHTTP.responseXML.documentElement;
		}

but there is no info in var x.
why?
Thanks in advanced.