Perhaps you should try some spelling variations:
hoc sach » hoc sinh, hoc cac, hoc anh
ban hanh » ban hang
dua tren » dung tren
tang ma » mang may, tang van
nang ma » sang ma, nang cao, mang may
sach ty » sach y, sach tu, sach thu
luc ban » duc ban, cuc ban, luc bat
ve cac » va cac, vien cac
vi dua » vi du, vi dum, vi lua
ve cau » ke cau, va cau, le cau

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: hoc sach ty ((nang ma) OR (tang ma)) hoa. hieu ((ve cau) or (ve cac)) luc ban hanh vi dua tren~.
• If you are trying to use Boolean operators, they must be ALL CAPS: hoc sach ty ((nang ma) OR (tang ma)) hoa. hieu ((ve cau) OR (ve cac)) luc ban hanh vi dua tren*.
• The words AND, OR and NOT may confuse the search; try adding quotes: "hoc sach ty ((nang ma) OR (tang ma)) hoa. hieu ((ve cau) or (ve cac)) luc ban hanh vi dua tren*".