Perhaps you should try some spelling variations:
vien cac » vien bach, vien dai, vien da
hang vai » hang va, hang tai, hang hai
ban hang » ngan hang
tu sach » thu sach, su sach, te sach
vai cua » dai cua, hai cua, lai cua
dua ban » dia ban, cua ban, qua ban
cua tre » cua te, cuu tre, cua triet
y nang » ky nang, ly nang, v nang
ve cac » va cac
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: tu sach y nang ((x hoi) or (o hoi)). hieu ((ve cac) OR (vien cac)) dua ban hang vai cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach y nang ((x hoi) OR (o hoi)). hieu ((ve cac) OR (vien cac)) dua ban hang vai cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach y nang ((x hoi) or (o hoi)). hieu ((ve cac) OR (vien cac)) dua ban hang vai cua tre".
• Adding a wildcard symbol may retrieve word variants: tu sach y nang ((x hoi) or (o hoi)). hieu ((ve cac) OR (vien cac)) dua ban hang vai cua tre*.