Using Collection in C#

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Collections.Specialized;

public partial class calc : System.Web.UI.Page
{
NameValueCollection d;
protected void Page_Load(object sender, EventArgs e)
{
d = new NameValueCollection();

d.Add("a1", "wao1");
d.Add("a2", "wao2");
d.Add("a3", "wao3");
}
protected void Button1_Click(object sender, EventArgs e)
{

System.Collections.IEnumerator ie = d.GetEnumerator();

String key;

while (ie.MoveNext())
{
key = ie.Current.ToString();
ListBox1.Items.Add(key + ":" + d.Get(key));
}

}
}