Perhaps you should try some spelling variations:
hoc sach » hoc sinh, hoc cac, hoc anh
hanh vai » hanh vi, hanh va, hanh tai
duy sang » duy van, duy can, duy anh
truc va » thuc vat, trung va
thuc va » thuc vat, thuc dan, thuc day
hieu ve » hieu va, hieu van
mai hoi » mai khoi, dai hoi, lai hoi
vai hoa » van hoa, va hoa, dai hoa
ve cau » ke cau, va cau, ve cac
y sang » _ sang

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

• Performing a fuzzy search may retrieve terms with similar spellings: hoc sach ((y sang) or (duy sang)) mai hoi. hieu ve cau ((truc va) OR (thuc va)) hanh vai hoa viet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: hoc sach ((y sang) OR (duy sang)) mai hoi. hieu ve cau ((truc va) OR (thuc va)) hanh vai hoa viet*.
• The words AND, OR and NOT may confuse the search; try adding quotes: "hoc sach ((y sang) or (duy sang)) mai hoi. hieu ve cau ((truc va) OR (thuc va)) hanh vai hoa viet*".