Perhaps you should try some spelling variations:
dau tren » dau tien, dat tren, dau tieng
hau treo » cau treo, cau theo, cau tren
hieu van » hieu va, thien van, lieu va
dang hai » dang khai, hang hai, dung hai
su sach » so sach, vu sach
sach lo » sach dao, sach doi, sach hoi
van cam » van nam, van lam, van cau
cao hoi » cau hoi, co hoi, cao hoc
lo nang » ho nang, ly nang, loai nang
tuc va » thuc va, truc va, duc va

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

• If you are trying to use Boolean operators, they must be ALL CAPS: su sach lo nang cao hoi. hieu van cam ((tuc va) OR (tuc xa)) dang hai ((hau treo) OR (dau tren))~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "su sach lo nang cao hoi. hieu van cam ((tuc va) or (tuc xa)) dang hai ((hau treo) OR (dau tren))~".
• Adding a wildcard symbol may retrieve word variants: su sach lo nang cao hoi. hieu van cam ((tuc va) or (tuc xa)) dang hai ((hau treo) OR (dau tren))*.