Perhaps you should try some spelling variations:
hieu van » hieu va, thien van, lieu va
danh hai » dang hai, lanh hai, manh hai
hoc sach » hoc sinh, hoc cac, hoc anh
so sach » so sanh, bo sach, co sach
thuc va » thuc vat, thuc dan, thuc day
van cau » van dau, van hau, van chat
tang ma » mang may, tang van
ca tren » cau tren, cu tren, la tren
ma hoi » mai hoi, xa hoi, ma hoa
tuc va » truc va, tuc xa, duc va
y tang » ky tang, 6 tang, 7 tang
hai ca » hai cua, hai ba, bai ca

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

• Performing a fuzzy search may retrieve terms with similar spellings: ((so sach) or (hoc sach)) y tang ma hoi. hieu van cau ((tuc va) or (thuc va)) danh hai ca tren~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((so sach) OR (hoc sach)) y tang ma hoi. hieu van cau ((tuc va) OR (thuc va)) danh hai ca tren.
• Adding a wildcard symbol may retrieve word variants: ((so sach) or (hoc sach)) y tang ma hoi. hieu van cau ((tuc va) or (thuc va)) danh hai ca tren*.