private void LoadLop()
{
LopDAO dao = new LopDAO();
string maCN = cbbChuyenNganh.SelectedValue.ToString();
dgvLop.DataSource = dao.GetByMaCN(maCN).Select(t => new
{
MaLop = t.MaLop,
TenLop = t.TenLop
}).ToList();
}