利用hashtable删除文本重复内容

Code
  //利用hashtable删除一个文本与另一个文本想重复内容
        private void button1_Click(object sender, EventArgs e)
        {
            //少数号码
            string phone = "";
            string path = "C:\\Documents and Settings\\Administrator\\桌面\\615.txt";
            FileStream fs = new FileStream(path, FileMode.Open);
            Hashtable ht = new Hashtable(); 
            using (StreamReader sr = new StreamReader(fs))
            {
                string line = sr.ReadLine();
                while (line != null)
                {
                    if (!ht.ContainsKey(line))
                    {
                        ht.Add(line,1);
                    }
                    line = sr.ReadLine();
                }
            }

            //多数号码
            string phone2="";
            string path2 = "C:\\Documents and Settings\\Administrator\\桌面\\123.txt";
            FileStream fs2 = new FileStream(path2, FileMode.Open);
            string content = "";
            using (StreamReader sr = new StreamReader(fs2))
            {
                content = sr.ReadToEnd();

                ICollection ic = ht.Keys;
                foreach (string s in ic)
                {
                    content = content.Replace(s+"\r\n", "");   
                }
 
            }

            //写入另一个文本
            string path3 = "C:\\Documents and Settings\\Administrator\\桌面\\111.txt";
            FileStream fs3 = new FileStream(path3, FileMode.OpenOrCreate);
            using (StreamWriter sw = new StreamWriter(fs3))
            {
                sw.WriteLine(content);
            }

        }