返回新闻中的所有图片，用|隔开

  public string MyGetImgUrl(string text)
    {
        StringBuilder str = new StringBuilder();
        string pat = @"<img\s+[^>]*\s*src\s*=\s*([']?)(?<url>\S+)'?[^>]*>";
        Regex r = new Regex(pat, RegexOptions.Compiled);
        Match m = r.Match(text.ToLower());
        while (m.Success)
        {
            Group g = m.Groups[2];
            //这里只取出图片的名字.ToString().Substring(g.ToString().LastIndexOf("/")+1)
            str.Append(g).Append("|");
            m = m.NextMatch();
        }
        return str.ToString().Replace("\"", "").TrimEnd('|');
    }