About drop down list!!

protected void Page_Load(object sender, EventArgs e)
{
    if (!IsPostBack)
    {
        DropDownList1.Items.Add("select");
        DropDownList1.Items.Add("Animal");
        DropDownList1.Items.Add("Vehicle");

    }
}
protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
{
    if (DropDownList1.SelectedIndex == 1)
    {
        DropDownList2.Items.Clear();
        DropDownList2.Visible = true;
        DropDownList2.Items.Add("cat");
    }
    else if(DropDownList1.SelectedIndex == 2)
    {
        DropDownList2.Items.Clear();
        DropDownList2.Visible = true;
        DropDownList2.Items.Add("car");
    }
    else if (DropDownList1.SelectedIndex == 0)
    {
        DropDownList2.Visible = false;
        DropDownList2.Items.Clear();
    }
}

<div>
    <asp:DropDownList ID="DropDownList1" runat="server" AutoPostBack="True"
        onselectedindexchanged="DropDownList1_SelectedIndexChanged">
    </asp:DropDownList>
    <asp:DropDownList ID="DropDownList2" runat="server" Visible="False">
    </asp:DropDownList>

</div>