Perhaps you should try some spelling variations:
tuan tai » toan tai, quan tai, tan tai
van tuan » van quan, van ban, anh tuan
cac duc » cac du, cao duc, cac nuoc
tai cua » thai cua, tai cuc, tri cua
cac dac » cac dan, cac dai, cac bac
cua tre » cua te, cuu tre, cua triet
sach ky » sac ky, sach ty, sach kem
hieu ve » hieu va, hieu van
nang o » nang co, nang ho, nang ro
o hoi » co hoi, o hoc, o hai

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 ky) or (sach y)) nang o hoi. hieu ve ((cac duc) OR (cac dac)) van tuan tai cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: te ((sach ky) OR (sach y)) nang o hoi. hieu ve ((cac duc) OR (cac dac)) van tuan tai cua tre*.
• The words AND, OR and NOT may confuse the search; try adding quotes: "te ((sach ky) or (sach y)) nang o hoi. hieu ve ((cac duc) OR (cac dac)) van tuan tai cua tre*".