C# - How To Get Empty Row In DropDownList

i have this citys in my database:

city1
city2
city3
city4

i what to see this in my DropDownList:

[empty]
city1
city2
city3
city4

this is my bind code:

SQL = "select distinct City from MyTbl order by City";
dsClass = new DataSet();
adp = new SqlDataAdapter(SQL, Conn);
adp.Fill(dsClass, "MyTbl");
adp.Dispose();
DropDownList3.DataSource = dsClass.Tables[0];
DropDownList3.DataTextField = dsClass.Tables[0].Columns[0].ColumnName.ToString();
DropDownList3.DataValueField = dsClass.Tables[0].Columns[0].ColumnName.ToString();
DropDownList3.DataBind();