selected value in dropdownlist and then show velue in another dropdownlist in asp.net

protected void CountryBind()
    {
        string sqlQuery = "Select * from Country";

        using (SqlConnection conn = new SqlConnection(conString))
        {
            conn.Open();
            DataSet ds = new DataSet();
            SqlDataAdapter da = new SqlDataAdapter(sqlQuery, conn);
            da.Fill(ds);
            ddlCountry.DataSource = ds;
            ddlCountry.DataBind();
            conn.Close();
        }
    }

protected void StateBind()
{
    string sqlQuery = "SELECT * FROM State " + " WHERE (CountryId = " + Convert.ToInt32(ddlCountry.SelectedValue) + " )";

    using (SqlConnection conn = new SqlConnection(conString))
    {
        conn.Open();
        DataSet ds = new DataSet();
        SqlDataAdapter da = new SqlDataAdapter(sqlQuery, conn);
        da.Fill(ds);
        ddlState.DataSource = ds;
        ddlState.DataBind();
        conn.Close();
    }
}

protected void CityBind()
{
    string sqlQuery = "SELECT * FROM City " + " WHERE (StateId = " + Convert.ToInt32(ddlState.SelectedValue) + " )";

    using (SqlConnection conn = new SqlConnection(conString))
    {
        conn.Open();
        DataSet ds = new DataSet();
        SqlDataAdapter da = new SqlDataAdapter(sqlQuery, conn);
        da.Fill(ds);
        ddlCity.DataSource = ds;
        ddlCity.DataBind();
        conn.Close();
    }
}

protected void ddlCountry_SelectedIndexChanged(object sender, EventArgs e)
{
    StateBind();
}
protected void ddlState_SelectedIndexChanged(object sender, EventArgs e)
{
    CityBind();
}