How to clear DropDownList Selected Item in ASP.Net

hI

I have dropdownlist in my page

in Page_load page I wrote below code

  if (!IsPostBack)
        {
     

            DDL1.Items.Insert(0, new ListItem("select city", "0"));
 DDL2.Items.Insert(0, new ListItem("select region", "0"));
            DdlDistrict.Items.Insert(0, new ListItem("select district", "0"));
}

and in this page I have btnInsert that when users click on it, it insert data in database

I want when users click on button all textboxs text be clear and all DDL selected Item clear so I set below code in btnInsert event

protected void imginsert_Click(object sender, ImageClickEventArgs e)
    {
            SqlCommand _cmd = new SqlCommand("insertFreg", _cn);
            _cmd.CommandType = CommandType.StoredProcedure;
            _cn.Open();

    
            _cmd.Parameters.AddWithValue("@address", txtsdd.Text);
            _cmd.Parameters.AddWithValue("@Aname", txtAname.Text);
            _cmd.Parameters.AddWithValue("@code",txtcode.Text);
        
            _cmd.Parameters.AddWithValue("@City", DDL1.SelectedItem.Text);
            _cmd.Parameters.AddWithValue("@Region", DDL2.SelectedItem.Text);
            _cmd.Parameters.AddWithValue("@District", DdlDistrict.SelectedItem.Text);
           
    


            int result = Convert.ToInt32(_cmd.ExecuteScalar());
            _cn.Close();


            if (result > 0)
            {
               
                LBLERROR.Text = "You data has been insert.";
                Txtadd.Text = " ";
                txtAname.Text = " ";
                txtcode.Text = " ";
            
               DDL1.Items.Insert(0, new ListItem("selectcity", "0"));
DDL2.Items.Insert(0, new ListItem("selectRegion", "0"));
DdlDistrict.Items.Insert(0, new ListItem("selectDistrict", "0"));
          
             


            }
            else
            {
                LBLERROR.Text = "ERROR";
            }    


    }

but here when I click on button it clear textboxs text but it didn't do any thing on Dropdownlist i.e

if I select 'Paris' from DDL1 when I click on button I want It show in ddl1 'Select city'

but it show 'Paris' again

what should I do?

Thanks