Perhaps you should try some spelling variations:
khanh toan » thanh toan, khanh thanh, khanh thuan
toan cau » toan cao, toan ban, toan tap
cau tren » cu tren, dau tren, ca tren
tu sach » thu sach, su sach, te sach
sach ky » sac ky, sach y, sach ty
hieu ve » hieu va, hieu van
duc van » duc tan, duc manh, duc phan
co hoi » co hoc, co loi
ve cac » va cac, vien cac
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) OR (duc va)) khanh toan cau 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) OR (duc va)) khanh toan cau 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) OR (duc va)) khanh toan cau tren".
• Adding a wildcard symbol may retrieve word variants: tu sach ky nang ((o hoc) or (co hoi)). hieu ve cac ((duc van) OR (duc va)) khanh toan cau tren*.