Perhaps you should try some spelling variations:
khanh toan » thanh toan, khanh thanh, khanh thuan
van khanh » van thanh, van hanh, van anh
cau tren » dau tren, ca tren, cau treo
tu sach » thu sach, su sach, te sach
sach ky » sac ky, sach y, sach ty
duc van » duc va, duc tan, duc manh
cac duc » cac du, cao duc, cac dac
cu tren » tu tren, dua tren
hieu ve » hieu va, hieu van
ve cac » va cac, vien cac
co hoi » co hoc, co loi
o hoc » co hoc, mo hoc, so hoc

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 nang ((o hoc) or (co hoi)). hieu ve cac duc van khanh toan ((cau tren) OR (cu tren))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ky nang ((o hoc) OR (co hoi)). hieu ve cac duc van khanh toan ((cau tren) OR (cu tren)).
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach ky nang ((o hoc) or (co hoi)). hieu ve cac duc van khanh toan ((cau tren) OR (cu tren))".
• Adding a wildcard symbol may retrieve word variants: tu sach ky nang ((o hoc) or (co hoi)). hieu ve cac duc van khanh toan ((cau tren) OR (cu tren))*.