void NapSinhVien()
{
DataTable dt = new DataTable();
bus = new BUS_Diem();
dt = bus.showdata_SinhVien();
var item = new Dictionary <string, string>();
foreach (DataRow dr in dt.Rows)
{
item.Add(dr["MaSV"].ToString(), dr["MaSV"].ToString() + " - " + dr["HoSV"].ToString() + " " + dr["TenSV"].ToString());
}
cbMaSV.DataSource = new BindingSource(item, null);
cbMaSV.DisplayMember = "Value";
cbMaSV.ValueMember = "Key";
}