private void ShowCourseComboBox()
        {
            aCourseBll = new CourseBLL();
            List <Course> nameCoursesList = aCourseBll.GetCourseNameList();

            foreach (Course course in nameCoursesList)
            {
                courseNameComboBox.Items.Add(course);
            }
            courseNameComboBox.DisplayMember = "Name";
        }