Perhaps you should try some spelling variations:
hieu viec » nhieu viec, hieu ve, sieu viet
ban hanh » ban hang
nuoc ban » nuoc san, quoc ban, buoc ban
cac nuoc » cap nuoc, hoc nuoc, dat nuoc
viec cac » vien cac, viec cua, viec lam
sach ty » sach y, sach tu, sach thu
nang ma » tang ma, sang ma, nang cao
vai cua » dai cua, lai cua, bai cua
hai cua » thai cua, dai cua, hoi cua
ma hoi » mai hoi, xa hoi, ma hoa
sac ky » cac ky, sai ky

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 ty) or (sac ky)) nang ma hoi. hieu viec cac nuoc ban hanh ((vai cua) OR (hai cua)) viet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu ((sach ty) OR (sac ky)) nang ma hoi. hieu viec cac nuoc ban hanh ((vai cua) OR (hai cua)) viet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu ((sach ty) or (sac ky)) nang ma hoi. hieu viec cac nuoc ban hanh ((vai cua) OR (hai cua)) viet".
• Adding a wildcard symbol may retrieve word variants: tu ((sach ty) or (sac ky)) nang ma hoi. hieu viec cac nuoc ban hanh ((vai cua) OR (hai cua)) viet*.