这样为什么替换不了??

C# code

 
 using System.Text.RegularExpressions; 
  
         protected void Button2_Click(object sender, EventArgs e) 
         { 
             string xx = this.TextBox1.Text.Trim(); 
             Regex.Replace("xx", "%Code%?", "4", RegexOptions.IgnoreCase); 
             Regex.Replace("xx", "%Rname%", "3", RegexOptions.IgnoreCase); 
             Regex.Replace("xx", "%Linkman%", "2", RegexOptions.IgnoreCase); 
             Regex.Replace("xx", "%Email%", "1", RegexOptions.IgnoreCase); 
             Response.Write(xx); 
         } 
  
 

[解决办法]
。。什么意思？
XX没有被重新赋值啊，XX的值又没有发生改变肯定没有效果三！