Perhaps you should try some spelling variations:
cac nuoc » cap nuoc, hoc nuoc, dat nuoc
hieu van » hieu va, thien van, lieu va
dua tren » dung tren
tu sach » thu sach, su sach, te sach
hieu ve » hieu va
danh vi » hanh vi, danh di, danh va
dinh vi » dinh ve, dinh viet, dinh tri
y nang » ky nang, ly nang, v nang

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 x ho. ((hieu ve) or (hieu van)) cac nuoc va ((danh vi) OR (dinh vi)) dua tren~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach y nang x ho. ((hieu ve) OR (hieu van)) cac nuoc va ((danh vi) OR (dinh vi)) dua tren.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach y nang x ho. ((hieu ve) or (hieu van)) cac nuoc va ((danh vi) OR (dinh vi)) dua tren".
• Adding a wildcard symbol may retrieve word variants: tu sach y nang x ho. ((hieu ve) or (hieu van)) cac nuoc va ((danh vi) OR (dinh vi)) dua tren*.