Perhaps you should try some spelling variations:
van thanh » ban thanh, van tuan
van hanh » ban hanh, van anh, van ban
cac duc » cac du, cao duc, cac dac
hieu ve » hieu va, hieu van
cuc tre » duc tre, cua tre, cuu tre
sach ky » sac ky, sach ty, sach kem
ve cac » va cac, vien cac
nang o » nang co, nang ho, nang ro
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 ky) or (sach y)) nang o hai. hieu ve cac duc ((van hanh) OR (van thanh)) tai cuc tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: te ((sach ky) OR (sach y)) nang o hai. hieu ve cac duc ((van hanh) OR (van thanh)) tai cuc tre*.
• The words AND, OR and NOT may confuse the search; try adding quotes: "te ((sach ky) or (sach y)) nang o hai. hieu ve cac duc ((van hanh) OR (van thanh)) tai cuc tre*".