Perhaps you should try some spelling variations:
hieu cac » hieu luc, hieu va, hieu van
hien cac » thien cac, vien cac, dien cac
danh vai » danh sai, danh va, doanh van
tu sach » thu sach, su sach, te sach
vai cua » dai cua, hai cua, lai cua
cua tre » cua te, cuu tre, cua triet
sach ky » sac ky, sach y, sach ty
nang xa » nang x, lang xa, nang ma
bo va » bao va, so va, co va
do va » do van, so 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 ky nang xa hoi. hieu ((hien cac) OR (hieu cac)) ((bo va) or (do va)) danh vai cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ky nang xa hoi. hieu ((hien cac) OR (hieu cac)) ((bo va) OR (do va)) danh vai cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach ky nang xa hoi. hieu ((hien cac) OR (hieu cac)) ((bo va) or (do va)) danh vai cua tre".
• Adding a wildcard symbol may retrieve word variants: tu sach ky nang xa hoi. hieu ((hien cac) OR (hieu cac)) ((bo va) or (do va)) danh vai cua tre*.