Perhaps you should try some spelling variations:
cao hoi » cau hoi, co hoi, cao hoc
cac duc » cao duc, cac dac, cac nuoc
sach ky » sac ky, sach y, sach kem
hieu ve » hieu va, hieu van
sach ty » sach y, sach tu, sach thu
cu tren » tu tren, dua tren
xa dan » ca dan, xa dai, va dan
ca cu » ca cua, cua cu, ca cau

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

• Performing a fuzzy search may retrieve terms with similar spellings: te ((sach ky) OR (sach ty)) nang cao hoi. hieu ve ((cac duc) or (cac du)) xa dan ca cu tren~.
• If you are trying to use Boolean operators, they must be ALL CAPS: te ((sach ky) OR (sach ty)) nang cao hoi. hieu ve ((cac duc) OR (cac du)) xa dan ca cu tren.
• The words AND, OR and NOT may confuse the search; try adding quotes: "te ((sach ky) OR (sach ty)) nang cao hoi. hieu ve ((cac duc) or (cac du)) xa dan ca cu tren".
• Adding a wildcard symbol may retrieve word variants: te ((sach ky) OR (sach ty)) nang cao hoi. hieu ve ((cac duc) or (cac du)) xa dan ca cu tren*.