Perhaps you should try some spelling variations:
dua tren » dung tren
hieu van » hieu va, thien van, lieu va
dan khai » dang khai, van khai, dang khoi
dan hai » doan hai, dang hai, van hai
truc va » thuc va, thuc vat, trung va
su sach » vu sach
so sach » so sanh, bo sach, co sach
cao hoi » cau hoi, co hoi, cao hoc
van cau » van dau, van hau, van chat
y nang » ky nang, ly nang, v nang

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) or (so sach)) y nang cao hoi. hieu van cau truc va ((dan hai) OR (dan khai)) dua tren~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((su sach) OR (so sach)) y nang cao hoi. hieu van cau truc va ((dan hai) OR (dan khai)) dua tren*.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((su sach) or (so sach)) y nang cao hoi. hieu van cau truc va ((dan hai) OR (dan khai)) dua tren*".