1. using System;
2. using System.Text.RegularExpressions;
3.                                        
4. public class Program
5. {
6.         public static void Main()
7.         {
8.                
9.                 string pattern = @"<b:ProductKeyStateID>.*</b:ProductKeyStateID>";
10.  
11.                 string input = RequestResult();
12.         RegexOptions options = RegexOptions.Multiline;
13.        
14.         foreach (Match m in Regex.Matches(input, pattern, options))
15.         {
16.             Console.WriteLine("'{0}' found at index {1}.", m.Value, m.Index);
17.         }
18.         }
19.        
20.         static String RequestResult(){
21.         string input = @"
22. --uuid:572ea376-67c5-4d00-bffd-549fc02b77d4+id=28
23. Content-ID: <http://tempuri.org/0>
24. Content-Transfer-Encoding: 8bit
25. Content-Type: application/xop+xml;charset=utf-8;type=application/soap+xml
26.  
27. <s:Envelope xmlns:s=http://www.w3.org/2003/05/soap-envelope xmlns:a=http://www.w3.org/2005/08/addressing><s:Header><a:Action s:mustUnderstand=1>http://tempuri.org/IOA30FFKIWCF/GetDPKStatusByWIP_SNResponse</a:Action></s:Header><s:Body><GetDPKStatusByWIP_SNResponse xmlns=http://tempuri.org/><GetDPKStatusByWIP_SNResult xmlns:b=com.compal.oa30 xmlns:i=http://www.w3.org/2001/XMLSchema-instance><b:Customer_Code i:nil=true/><b:ErrorDescription/><b:OEMPartNumber i:nil=true/><b:Plant_Code i:nil=true/><b:Product i:nil=true/><b:ProductKey>MBWCR-43N77-6GDK6-KQV6T-PDK2M</b:ProductKey><b:ProductKeyID>3424334527449</b:ProductKeyID><b:ProductKeyStateID>3</b:ProductKeyStateID><b:Status>true</b:Status><b:WIP_SN>4003189900003</b:WIP_SN></GetDPKStatusByWIP_SNResult></GetDPKStatusByWIP_SNResponse></s:Body></s:Envelope>
28. --uuid:572ea376-67c5-4d00-bffd-549fc02b77d4+id=28--
29. ";
30.                 return input;
31.         }
32.        
33. }