Perhaps you should try some spelling variations:
quoc ban » quoc bao, quoc lan, quoc quan
cam quoc » cac quoc, cao quoc, nam quoc
su sach » so sach, vu sach
hanh ve » hanh vi, hanh va, hanh kem
hieu va » lieu va, hieu qua
cua tre » cua te, cuu tre, cua triet
sach v » sach va, sach y, sach 2
anh ve » anh va, anh viet, thanh ve
v nang » va nang, vu nang, van nang
va cam » va cham, va cac, va cao
o hoi » co hoi, o hoc, o hai
x hoi » xa hoi, x ho, 5 hoi

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

• Performing a fuzzy search may retrieve terms with similar spellings: su sach v nang ((x hoi) or (o hoi)). hieu va cam quoc ban ((anh ve) OR (hanh ve)) cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su sach v nang ((x hoi) OR (o hoi)). hieu va cam quoc ban ((anh ve) OR (hanh ve)) cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "su sach v nang ((x hoi) or (o hoi)). hieu va cam quoc ban ((anh ve) OR (hanh ve)) cua tre".
• Adding a wildcard symbol may retrieve word variants: su sach v nang ((x hoi) or (o hoi)). hieu va cam quoc ban ((anh ve) OR (hanh ve)) cua tre*.