C#实现HTTP POST请求的一个问题

/// <summary>
        ///  抓取网站内容（项目需求进行更改，抓folktel字段）
        /// </summary>
        /// <param name="webUrl">网站地址</param>
        /// <param name="cookie">cookie</param>
        /// <returns></returns>
        public static string GetWebSourceFile(string webUrl,string cookie)
        {
            WebClient webClient = new WebClient();
            webClient.Headers.Add("Cookie", cookie);
            webClient.Credentials = CredentialCache.DefaultCredentials; 
            Stream stream = webClient.OpenRead(webUrl);
            StreamReader reader = new StreamReader(stream);
            string content = reader.ReadToEnd();
            reader.Close();
            stream.Close();
            return content;
            
        }