Perhaps you should try some spelling variations:
van hanh » van thanh, ban hanh, van anh
van nang » van quang, van ban, van dong
truc van » truc va, thuc van, truc ban
cam truc » cau truc, nam truc, lam truoc
su sach » vu sach
hanh de » hanh ve, hanh kem
hieu ve » hieu va, hieu van
cua tre » cua te, cuu tre, cua triet
so sach » so sanh, bo sach, co sach
ve cam » ve cham, ve cac, va cam
de cua » le cua, te cua, dieu cua
o hoi » co hoi, o hoc, o hoa
o hai » co hai, so hai, o lai

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) OR (so sach)) van nang ((o hoi) or (o hai)). hieu ve cam truc van hanh de cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((su sach) OR (so sach)) van nang ((o hoi) OR (o hai)). hieu ve cam truc van hanh de cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((su sach) OR (so sach)) van nang ((o hoi) or (o hai)). hieu ve cam truc van hanh de cua tre".
• Adding a wildcard symbol may retrieve word variants: ((su sach) OR (so sach)) van nang ((o hoi) or (o hai)). hieu ve cam truc van hanh de cua tre*.