Creating a chained dropdownlist using AJAX and XML

using System;
using System.Data;

public partial class _Default : System.Web.UI.Page 
{
    DataSet ds = new DataSet();
    protected void Page_Load(object sender, EventArgs e)
    {
        if (Cache["Motos"] == null)
        {
            ds.ReadXml(Server.MapPath("~/XMLFiles/Motors.xml"), XmlReadMode.InferSchema);
            Cache.Insert("Motos", ds);
        }
        else
            ds = (DataSet)Cache["Motos"];
    }

    protected void drpMain_SelectedIndexChanged(object sender, EventArgs e)
    {
        System.Threading.Thread.Sleep(1200);

        if (drpMain.SelectedValue == "0")
        {
            drpMoto.Items.Clear();
            drpBrand.Items.Clear();
            drpMoto.Enabled = false;
            drpBrand.Enabled = false;
            btnGo.Enabled = false;
        }
        else if (drpMain.SelectedValue == "1")
        {
            drpMoto.DataTextField = "mcname";
            drpMoto.DataValueField = "mcid";
            drpMoto.DataSource = ds.Tables["motoc"];
            drpMoto.DataBind();
            drpMoto.Enabled = true;
            drpBrand.Items.Clear();
            drpBrand.Enabled = false;
            btnGo.Enabled = false;
        }
        else if (drpMain.SelectedValue == "2")
        {
            drpMoto.DataTextField = "mbname";
            drpMoto.DataValueField = "mbid";
            drpMoto.DataSource = ds.Tables["motob"];
            drpMoto.DataBind();
            drpMoto.Enabled = true;
            drpBrand.Items.Clear();
            drpBrand.Enabled = false;
            btnGo.Enabled = false;
        }
    }

    protected void drpMoto_SelectedIndexChanged(object sender, EventArgs e)
    {
        System.Threading.Thread.Sleep(1200);

        if (drpMoto.SelectedItem.Value == "0")
        {
            drpBrand.Items.Clear();
            drpBrand.Enabled = false;
            btnGo.Enabled = false;
        }
        else if (drpMain.SelectedValue == "1" && drpMoto.SelectedItem.Value != "0")
        {
            DataView dView = new DataView(ds.Tables["motocb"]);
            dView.RowFilter = "mcid='" + drpMoto.SelectedValue.Trim() + "'";
            dView.Sort = "mcbname asc";
            drpBrand.DataTextField = "mcbname";
            drpBrand.DataValueField = "mcbid";
            drpBrand.DataSource = dView;
            drpBrand.DataBind();
            drpBrand.Enabled = true;
            btnGo.Enabled = true;
        }
        else if (drpMain.SelectedValue == "2" && drpMoto.SelectedItem.Value != "0")
        {
            DataView dView = new DataView(ds.Tables["motobb"]);
            dView.RowFilter = "mbid='" + drpMoto.SelectedValue.Trim() + "'";
            dView.Sort = "mbbname asc";
            drpBrand.DataTextField = "mbbname";
            drpBrand.DataValueField = "mbbid";
            drpBrand.DataSource = dView;
            drpBrand.DataBind();
            drpBrand.Enabled = true;
            btnGo.Enabled = true;
        }
    }

    protected void btnGo_OnClick(object sender, EventArgs e)
    {
        lblResult.Text = "Searched for: <b>" + drpBrand.SelectedItem.Text.Replace("(","").Replace(")","") + " " + drpMoto.SelectedItem.Text + " " + drpMain.SelectedItem.Text.Replace("s","") + "(s)</b>";
    }
}