Get webpage's script problem

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I have the following code snippet:

WebRequest request = WebRequest.Create(URL);
request.Method = "GET";
request.ContentType = "text/xml";

WebResponse response = request.GetResponse();
System.IO.Stream stream = response.GetResponseStream();
System.IO.StreamReader streamReader = new System.IO.StreamReader(stream);
String document = streamReader.ReadToEnd();

I have got the HTML content and javascript successful but it lack of the
javascript inside the <!-- --tags.

How can I solve this problem?
Thanks for your help!
Hung