buttons click event is fire accurately but radiobuttonlist controls SelectIndexChange

[C# Programming]

protected void Page_Init(object sender, EventArgs e)
{
RadioButtonList rbl = new RadioButtonList();
rbl.ID = "rbl1";
rbl.Items.Add("a");
rbl.Items.Add("b");
PlaceHolder1.Controls.Add(rbl);
rbl.SelectedIndexChanged += new EventHandler(rbl_SelectedIndexChanged);
Button btn = new Button();
btn.ID = "btn1";
btn.Text = "Button";
PlaceHolder2.Controls.Add(btn);
btn.Click += new EventHandler(btn_Click);
}
protected void Page_Load(object sender, EventArgs e)
{
}
private void btn_Click(object s, EventArgs e)
{
Label2.Text = "buttons click event fired";
}
private void rbl_SelectedIndexChanged(object s, EventArgs e)
{
Label1.Text="radiobuttonlist control selectedindexchanged event fired";
//RadioButtonList rbl2=(RadioButtonList)s;
//Label1.Text = rbl2.SelectedValue;
}

Jyoti Goel