Perhaps you should try some spelling variations:
dai moi » doi moi
sach ky » sac ky, sach y, sach ty
tu sach » thu sach, su sach, te sach
dai hoi » dai hoc, dai hai
ky tang » ky nang, ky dang, kho tang
cua tre » cua te, cuu tre, cua triet
tro va » tao va, tho va, tro ba
va dau » va dao
dau di » da di, dau da, dau do
di cua » dai cua, doi cua, de cua

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 tang ((dai hoi) OR (dai moi)). ((lieu va) or (hieu qua)) cac tro va dau di cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ky tang ((dai hoi) OR (dai moi)). ((lieu va) OR (hieu qua)) cac tro va dau di cua tre*.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach ky tang ((dai hoi) OR (dai moi)). ((lieu va) or (hieu qua)) cac tro va dau di cua tre*".