Perhaps you should try some spelling variations:
van thanh » ban thanh, van tuan
hieu van » hieu va, thien van, lieu va
van hanh » ban hanh, van anh, van ban
cau duc » cao duc, cau luc, chu duc
van cau » van dau, van hau, van chat
sach ky » sac ky, sach y, sach kem
sach ty » sach y, sach tu, sach thu
cua tre » cua te, cuu tre, cua triet
va cua » va chua, via cua, ca cua
x hoi » xa hoi, o hoi, x ho

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 ty)) nang x hoi. hieu van cau duc ((van hanh) OR (van thanh)) va cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: te ((sach ky) OR (sach ty)) nang x hoi. hieu van cau duc ((van hanh) OR (van thanh)) va cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "te ((sach ky) or (sach ty)) nang x hoi. hieu van cau duc ((van hanh) OR (van thanh)) va cua tre".
• Adding a wildcard symbol may retrieve word variants: te ((sach ky) or (sach ty)) nang x hoi. hieu van cau duc ((van hanh) OR (van thanh)) va cua tre*.