private void loadCourses()
        {
            comboBox2.Items.Clear();
            Online_Exame exam = new Online_Exame();
            var          cour = exam.getInsCourses(inst);

            foreach (var item in cour)
            {
                comboBox2.Items.Add($"{item.C_id} , {item.C_name}");
            }
        }