protected void Page_Load(object sender, EventArgs e)
 {
     List<Class> classesList = new List<Class>();
     _helper = new SqlHelper(StudentsDatabase.GetInstance());
     classesList = _helper.GetClasses();
     foreach(Class c in classesList){
         ddlClasses.Items.Add(c.ToString());
     }
 }
 public StudentsDataResponder(SqlHelper helper)
 {
     this._helper = helper;
 }