Perhaps you should try some spelling variations:
dang xay » dang van, van xay
tang tai » hang tai, dung tai, sang tao
tu sach » thu sach, su sach, te sach
xay hoi » xa hoi, tay hoi, cay phoi
hieu va » lieu va, hieu qua
thue va » thuc va, thuyet va, thuat va
tai cua » thai cua, tai cuc, tri cua
cua tre » cua te, cuu tre, cua triet
sach o » sach lo, sac o, sach y
o dang » xo dang, do dang, so dang
va cam » va cham, va cac, va cao

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 o dang xay hoi. hieu va cam ((thue va) or (thuc vat)) tang tai cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach o dang xay hoi. hieu va cam ((thue va) OR (thuc vat)) tang tai cua tre.
• Adding a wildcard symbol may retrieve word variants: tu sach o dang xay hoi. hieu va cam ((thue va) or (thuc vat)) tang tai cua tre*.