private void ThemHocSinhVaoLop_Load(object sender, EventArgs e)
{
List <string> lops = Lbus.GetDanhSachLopString();
lops.Insert(0, "None");
comboBoxLop.DataSource = lops;
comboBoxGioiTinh.SelectedIndex = 0;
hocSinhs = HSbus.XemTatCaHS();
dataGridViewDS_HS.DataSource = hocSinhs;
AddCotCheckbox();
CheckHocSinh();
}