Perhaps you should try some spelling variations:
hieu van » thien van, lieu va, hieu ve
cac quoc » cac nuoc, cac cuoc, cao quoc
quoc ban » quoc bao, quoc lan, quoc quan
tu sach » thu sach, su sach, te sach
sach ky » sac ky, sach y, sach ty
nang xa » nang x, lang xa, nang ma
hieu va » lieu va, hieu qua
benh vi » benh ve, benh li, kenh vi
benh va » benh ve, benh dai, benh tai
cua tre » cua te, cuu tre, cua triet

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 xa hoi. ((hieu van) or (hieu va)) cac quoc ban ((benh vi) OR (benh va)) cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ky nang xa hoi. ((hieu van) OR (hieu va)) cac quoc ban ((benh vi) OR (benh va)) cua tre*.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach ky nang xa hoi. ((hieu van) or (hieu va)) cac quoc ban ((benh vi) OR (benh va)) cua tre*".