Perhaps you should try some spelling variations:
cuu tre » cau tren, cau treo
sach ky » sac ky, sach ty, sach kem
hieu ve » hieu va, hieu van
cua tre » cua te, cua triet, dua tren
cac su » cach su, cac sau, cac du
va dao » ca dao
dao vi » dao voi, dao ve, dao va
ve cac » va cac, vien cac
x hoi » xa hoi, o hoi, x ho
su va » su van, tu va

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

• Performing a fuzzy search may retrieve terms with similar spellings: tu ((sach ky) or (sach y)) nang x hoi. hieu ve cac su va dao vi ((cuu tre) OR (cua tre))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu ((sach ky) OR (sach y)) nang x hoi. hieu ve cac su va dao vi ((cuu tre) OR (cua tre)).
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu ((sach ky) or (sach y)) nang x hoi. hieu ve cac su va dao vi ((cuu tre) OR (cua tre))".
• Adding a wildcard symbol may retrieve word variants: tu ((sach ky) or (sach y)) nang x hoi. hieu ve cac su va dao vi ((cuu tre) OR (cua tre))*.