HttpWebRequest request = (HttpWebRequest)HttpWebRequest.Create(strUrl);
                    //接收的起始位置及接收的长度
                    request.AddRange(formm.filestartw[threadh],formm.filestartw[threadh] + formm.filesizew[threadh]);
                   // MessageBox.Show("线程" + threadh.ToString() + "开始接受");
                    HttpWebResponse response = (HttpWebResponse)request.GetResponse();
                    MessageBox.Show("线程" + formm.filestartw[threadh].ToString() + "开始接受");
                    ns = response.GetResponseStream();//获得接收流

为什么