Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
sach ly » sach y, sach lo, sach ty
lua tre » cua tre, dua tren, luat tri
doan vi » doan va, don vi, doan thi
va doan » va doanh, van doan, va dan
cac luc » cau luc, coc luc, cac nuoc
ly hang » ly quang
hieu ve » hieu va, hieu van
luy tre » luyen tre
ve cac » va cac, vien cac
luc va » duc va, tuc va, loc va
hang o » hang do, hang o2, hoang o
o hoi » co hoi, o hoc, o hai

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

• Performing a fuzzy search may retrieve terms with similar spellings: toc sach ly hang o hoi. hieu ve cac luc va doan vi ((lua tre) or (luy tre))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach ly hang o hoi. hieu ve cac luc va doan vi ((lua tre) OR (luy tre)).
• Adding a wildcard symbol may retrieve word variants: toc sach ly hang o hoi. hieu ve cac luc va doan vi ((lua tre) or (luy tre))*.