Drop Down List with no item selected

I have a drop down list that loads and has the first item [0] selected.  I tried setting the selected index to -1 but it still shows as 0.  Is there any way to have it so none of the items in the drop down list are selected so that it will force the user to select one?  Here is the code for binding the data from the database:

DA_Class DAobject = new DA_Class();
ddl.DataSource = DAobject.GetItems();
ddl.DataTextField = "Description";
ddl.DataValueField = "ID";
ddl.DataBind();

ddl.SelectedIndex = -1;

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