HttpWebRequest第一次请求为什么很慢

Delphi新人学C#
HttpWebResponse Response = (HttpWebResponse)Request.GetResponse();
为什么第一次请求，等半天才回执，另求封装好的Http请求类，类似Delphi的IdHTTP组件的````要支持cookie，看能求到不，我自己写的感觉很不像样namespace xxxxxx
{   
    class IdHTTP
    {
        public string ResponseText;
        public int ResponseCode;
        public string Charset;
        public HttpWebRequest Request;
        public bool KeepAlive;
        public string UserAgent;
        public string ContentType;        public string GetHTML(string URL, string PostData, bool isPost)
        {
            Request = (HttpWebRequest)WebRequest.Create(URL);
            Request.Method = isPost ? "POST" : "GET";
            Request.KeepAlive = KeepAlive;
            Request.UserAgent = UserAgent;
            Request.ContentType = ContentType;            try
            {
                if (isPost)
                {
                    //写入POST参数
                    Encoding encoding = Encoding.Default; 
                    byte[] buffer = encoding.GetBytes(PostData);
                    Request.ContentLength = buffer.Length;
                    Request.GetRequestStream().Write(buffer, 0, buffer.Length);
                }
                //发送请求
                HttpWebResponse Response = (HttpWebResponse)Request.GetResponse();
                StreamReader Reader = new StreamReader(Response.GetResponseStream(), Encoding.GetEncoding(Charset));
                string result = Reader.ReadToEnd();
                Response.Close();
                Reader.Close();
                ResponseCode = Convert.ToInt32(Response.StatusCode);
                ResponseText = Response.StatusDescription;
                return result;
     
            }
            catch (WebException e)
            {
                ResponseCode = Convert.ToInt32(((HttpWebResponse)e.Response).StatusCode);
                ResponseText = ((HttpWebResponse)e.Response).StatusDescription;
                return ResponseText;
            }   
        }        public string Get(string URL)
        {
            return GetHTML(URL, "", false);
        }        public string Post(string URL, string PostData)
        {
            return GetHTML(URL, PostData, true);
        }
    }
}