private void AddStudentToClass_Load(object sender, EventArgs e)
{
cbClass.DisplayMember = "ClassName";
cbClass.ValueMember = "ClassID";
cbClass.DataSource = ClassList.GetAllClass();
cbClass.SelectedIndex = 0;
cbStudent.DisplayMember = "StudentName";
cbStudent.ValueMember = "StudentID";
cbStudent.DataSource = StudentList.GetAllStudent();
cbStudent.SelectedIndex = 0;
}