duplication in dropdown item ASP.net

Question

I have problem with DropDownList in ASP.NET 1, 2.

Each time I select an item, the items in the list are repeated 3.

It appears fine the first time of selection only.

my code C#

protected void Page_Load(object sender, EventArgs e)
{
    CRUD myCrud = new CRUD();
    string mySql = (@" my query here   ");
    SqlDataReader dr = myCrud.getDrPassSql(mySql);
    DropDownList1.DataSource = dr;
    DropDownList1.DataTextField = "type";
    DropDownList1.DataValueField = "id";
    DropDownList1.DataSource = dr;
    DropDownList1.DataBind();

    CRUD myCrud2 = new CRUD();
    string mySql2 = (@" my another query based on the type selected above  ");
    SqlDataReader dr2 = myCrud2.getDrPassSql(mySql2);
    DropDownList3.DataSource = dr2;
    DropDownList3.DataTextField = "NameEN";
    DropDownList3.DataSource = dr2;
    DropDownList3.DataBind();
}

Answer 1

As suggested in comments:

   protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            // your above page load code goes here
        }
    }