Perhaps you should try some spelling variations:
doc sach » toc sach, nuoc sach, dac sac
hoc sach » hoc sinh, hoc cac, hoc anh
hang tai » hang va, dung tai
van hang » van khang, van hoang, van thang
tai cua » thai cua, tai cuc, tri cua
xuc van » duc van, luc van, vuc van
cac xuc » cam xuc, cac nuoc, chat xuc
hieu va » lieu va, hieu qua
cua tre » cua te, cuu tre, cua triet
x hoi » xa hoi, x ho, 5 hoi
o hoi » co hoi, o hoc, o hai

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: ((doc sach) or (hoc sach)) ky nang ((x hoi) OR (o hoi)). hieu va cac xuc van hang tai cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((doc sach) OR (hoc sach)) ky nang ((x hoi) OR (o hoi)). hieu va cac xuc van hang tai cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((doc sach) or (hoc sach)) ky nang ((x hoi) OR (o hoi)). hieu va cac xuc van hang tai cua tre".
• Adding a wildcard symbol may retrieve word variants: ((doc sach) or (hoc sach)) ky nang ((x hoi) OR (o hoi)). hieu va cac xuc van hang tai cua tre*.