Perhaps you should try some spelling variations:
van hanh » van thanh, ban hanh, van anh
nang xa » nang x, nang ma, mang xa
lang xa » lang ha, dang xay, lang van
qua cac » cua cac
cac hoc » cach hoc, cac hop, bac hoc
va hanh » va thanh, va danh, ban hanh
te cac » tu cac, ve cac, te cao
cua te » cua tu

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

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