Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
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
luy tre » luyen tre
hieu ve » hieu va, hieu van
ly nang » ky nang, ly hang, ly vang
luc va » duc va, tuc va, loc va
ve cac » va cac, vien cac
x hoi » xa hoi, o hoi, x ho

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

• Performing a fuzzy search may retrieve terms with similar spellings: ((te sach) OR (toc sach)) ly nang x 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: ((te sach) OR (toc sach)) ly nang x hoi. hieu ve cac luc va doan vi ((lua tre) OR (luy tre)).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((te sach) OR (toc sach)) ly nang x hoi. hieu ve cac luc va doan vi ((lua tre) or (luy tre))".
• Adding a wildcard symbol may retrieve word variants: ((te sach) OR (toc sach)) ly nang x hoi. hieu ve cac luc va doan vi ((lua tre) or (luy tre))*.