Perhaps you should try some spelling variations:
sach thu » sach thue, sach thieu, sach tham
thu nang » thi nang, thu hang, thu bang
van hanh » van thanh, ban hanh, van anh
te sach » toc sach
hieu va » lieu va, hieu qua
cua tre » cua te, cuu tre, cua triet
nang o » nang co, nang ho, nang ro
cac bo » bac bo
cac co » cac cong
vi cua » vai cua, di cua
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: te sach thu nang o hai. hieu va ((cac bo) or (cac co)) van hanh vi cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: te sach thu nang o hai. hieu va ((cac bo) OR (cac co)) van hanh vi cua tre.
• Adding a wildcard symbol may retrieve word variants: te sach thu nang o hai. hieu va ((cac bo) or (cac co)) van hanh vi cua tre*.