Populate DropDownList Dynamically in ASP.NET (Country-State-District-City)

How to Make a Complete Dropdown and Prevent Inserting Dummy Data from Form.
Disable other Controls when Clicked back to Parent Control:
Drop Down Sequence:
OnLoad
Load Country
On-Change
Load State according to Country
On-Change
Load Dists in State
On-Change
List Cities in Dist.

Code:

 protected void ddlCountry_SelectedIndexChanged(object sender, EventArgs e)
  {
   ddlState.DataSource = res.States(Convert.ToInt16(ddlCountry.SelectedValue));
   ddlState.DataTextField = "StateName";
   ddlState.DataValueField = "StateID";
   ddlState.DataBind(); 
   ddlState.Items.Insert(0, "Select");
   ddlDist.Enabled = false;
   ddlCity.Enabled = false;
  }
 protected void ddlState_SelectedIndexChanged(object sender, EventArgs e)
    
  {
   ddlDist.DataSource = res.Districts(Convert.ToInt16(ddlState.SelectedValue));
   ddlDist.DataTextField = "DistName";
   ddlDist.DataValueField = "DistID";
   ddlDist.DataBind();
   ddlDist.Items.Insert(0, "Select");
   ddlDist.Enabled = true;
   ddlCity.Enabled = false;
  }
 protected void ddlDist_SelectedIndexChanged(object sender, EventArgs e)
  {
   ddlCity.DataSource = res.Cities(Convert.ToInt16(ddlDist.SelectedValue));
   ddlCity.DataTextField = "CityName";
   ddlCity.DataValueField = "CityID";
   ddlCity.DataBind();
   ddlCity.Items.Insert(0, "Select");
   ddlCity.Enabled = true;
  }

Preview:
John Bhatt
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