Perhaps you should try some spelling variations:
khanh toan » thanh toan, khanh thanh, khanh thuan
van khanh » van thanh, van hanh, van anh
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
cac duc » cac du, cao duc, cac dac
duc van » duc va, duc tan, duc manh
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 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 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 khanh toan cau tren*.