private void BtnStudentHomeETT_Click(object sender, EventArgs e)
        {
            StudentExam seh = new StudentExam();

            this.Hide();
            seh.ShowDialog();
        }
        private void MngExmBtn_Click(object sender, System.EventArgs e)
        {
            StudentExam seh = new StudentExam();

            this.Hide();
            seh.ShowDialog();
        }