Perhaps you should try some spelling variations:
khanh thai » nhanh thai, khanh thanh, khanh thuan
van khanh » van thanh, van hanh, van anh
tu sach » thu sach, su sach, te sach
thai cu » thai cua, thai xu, thi cu
duc van » duc va, duc tan, duc manh
cac duc » cac du, cao duc, cac dac
hieu ve » hieu va, hieu van
cu tren » tu tren, dua tren
sach ky » sac ky, sach y, sach ty
ve cac » va cac, vien cac
so hai » son hai, su hai, so ha
o hoc » co hoc, mo hoc, so hoc
o hoi » co hoi, o hai, 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 ky nang ((((o hoi) or (o hoc))) or (so hai)). hieu ve cac duc van khanh thai cu tren~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ky nang ((((o hoi) OR (o hoc))) OR (so hai)). hieu ve cac duc van khanh thai cu tren.
• Adding a wildcard symbol may retrieve word variants: tu sach ky nang ((((o hoi) or (o hoc))) or (so hai)). hieu ve cac duc van khanh thai cu tren*.