Perhaps you should try some spelling variations:
tu sach » thu sach, su sach, te sach
cach tu » cach thuc
sach ky » sac ky, sach y, sach ty
hieu ve » hieu va, hieu van
cua tre » cua te, cuu tre, cua triet
cac tu » cac thu, cac du, tac tu
va dan » ca dan, va dao, va dau
dan va » doan va, dan ca, ban va
va cua » va chua, via cua, ca cua
o hai » co hai, so hai, o lai
o hoi » co hoi, o hoc, o hoa

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 ky nang ((o hoi) or (o hai)). hieu ve ((cac tu) or (cach tu)) va dan va cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ky nang ((o hoi) OR (o hai)). hieu ve ((cac tu) OR (cach tu)) va dan va cua tre.
• Adding a wildcard symbol may retrieve word variants: tu sach ky nang ((o hoi) or (o hai)). hieu ve ((cac tu) or (cach tu)) va dan va cua tre*.