void loadcbb()
{
TaiLieu tl = new TaiLieu();
cbbTenChiTiet.DataSource = tl.loadcbbtentheloai();
cbbTacGia.DataSource = tl.loadcbbtacgia();
cbbNhaXB.DataSource = tl.loadcbbnxb();
cbbNhaCC.DataSource = tl.loadcbbncc();
cbbViTri.DataSource = tl.loadcbbvitri();
}