Perhaps you should try some spelling variations:
cac truc » cau truc, cac tru, cac trung
va hang » van hang, va nang, va lang
truc va » thuc va, thuc vat, trung va
hieu va » lieu va, hieu qua
su sach » so sach, vu sach
vu nang » vuc nang, va nang, vu dang
v nang » va nang, van nang, voi nang
don su » dong su, dan su, den su

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

• Performing a fuzzy search may retrieve terms with similar spellings: su sach ((v nang) or (vu nang)) xa hoi. hieu va cac truc va hang ((down su) OR (don su)) tien~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su sach ((v nang) OR (vu nang)) xa hoi. hieu va cac truc va hang ((down su) OR (don su)) tien.
• The words AND, OR and NOT may confuse the search; try adding quotes: "su sach ((v nang) or (vu nang)) xa hoi. hieu va cac truc va hang ((down su) OR (don su)) tien".
• Adding a wildcard symbol may retrieve word variants: su sach ((v nang) or (vu nang)) xa hoi. hieu va cac truc va hang ((down su) OR (don su)) tien*.