Perhaps you should try some spelling variations:
khanh thi » nhanh thi, khanh thu, nhanh thai
van khanh » van thanh, van hanh, van anh
tu sach » thu sach, su sach, te sach
cac luc » cau luc, coc luc, cac nuoc
cuc tre » duc tre, cua tre, cuc thue
luc van » luoc van, luu van, duc van
cuu tre » cua tre, cau tren, cau treo
hieu ve » hieu va, hieu van
y nang » ky nang, ly nang, v nang
ve cac » va cac, vien cac
o hai » co hai, so hai, o lai
o hoi » co hoi, o hoc, o hoa

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 y nang ((o hoi) or (o hai)). hieu ve cac luc van khanh thi ((cuc tre) OR (cuu tre))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach y nang ((o hoi) OR (o hai)). hieu ve cac luc van khanh thi ((cuc tre) OR (cuu tre)).
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach y nang ((o hoi) or (o hai)). hieu ve cac luc van khanh thi ((cuc tre) OR (cuu tre))".
• Adding a wildcard symbol may retrieve word variants: tu sach y nang ((o hoi) or (o hai)). hieu ve cac luc van khanh thi ((cuc tre) OR (cuu tre))*.