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

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