Web Forms :: How To Clear DropDownList Selected Item

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);

[Code] .....

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?