Perhaps you should try some spelling variations:
dau tren » dau tien, dat tren, dau tieng
sach ky » sac ky, sach ty, sach kem
hieu va » lieu va, hieu qua
cac luc » cau luc, coc luc, cac nuoc
cu tren » tu tren, dua tren
luc va » duc va, tuc va, loc va
va dan » ca dan, va dao, va dau
dan vi » doan vi, don vi, dan va

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

• Performing a fuzzy search may retrieve terms with similar spellings: tu ((sach ky) OR (sach y)) nang x ho. hieu va cac luc va dan vi ((cu tren) or (dau tren))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu ((sach ky) OR (sach y)) nang x ho. hieu va cac luc va dan vi ((cu tren) OR (dau tren)).
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu ((sach ky) OR (sach y)) nang x ho. hieu va cac luc va dan vi ((cu tren) or (dau tren))".
• Adding a wildcard symbol may retrieve word variants: tu ((sach ky) OR (sach y)) nang x ho. hieu va cac luc va dan vi ((cu tren) or (dau tren))*.