Perhaps you should try some spelling variations:
dau tren » dau tien, dat tren, dau tieng
cau tren » cu tren, ca tren, cau treo
van hanh » van thanh, ban hanh, van anh
cham tu » pham tu, cam tu, chai tu
vu cham » va cham, vu kham, tu cham
tu sach » thu sach, su sach, te sach
lang ha » long ha
nang xa » nang x, lang xa, nang ma
hieu vu » hieu va, hieu ve, hieu su
tu van » tu va

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 y ((nang xa) or (lang ha)) hoi. hieu vu cham tu van hanh vi ((cau tren) OR (dau tren))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach y ((nang xa) OR (lang ha)) hoi. hieu vu cham tu van hanh vi ((cau tren) OR (dau tren)).
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach y ((nang xa) or (lang ha)) hoi. hieu vu cham tu van hanh vi ((cau tren) OR (dau tren))".
• Adding a wildcard symbol may retrieve word variants: tu sach y ((nang xa) or (lang ha)) hoi. hieu vu cham tu van hanh vi ((cau tren) OR (dau tren))*.