Perhaps you should try some spelling variations:
hoang van » hang va
hieu cua » hieu qua, dieu cua, bieu cua
nang xa » nang x, lang xa, nang ma
cac hoc » cach hoc, cac hop, bac hoc
va hanh » van hanh, va thanh, va danh
tai cua » thai cua, tai cuc, dai cua
te sac » te sach, te cac, te san
sac ky » cac ky, sai ky

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: te sac ky ((nang xa) or (hoang van)) hoi. hieu cua cac hoc va hanh ((tai cua) OR (tri cua)) te~.
• If you are trying to use Boolean operators, they must be ALL CAPS: te sac ky ((nang xa) OR (hoang van)) hoi. hieu cua cac hoc va hanh ((tai cua) OR (tri cua)) te*.
• The words AND, OR and NOT may confuse the search; try adding quotes: "te sac ky ((nang xa) or (hoang van)) hoi. hieu cua cac hoc va hanh ((tai cua) OR (tri cua)) te*".