Perhaps you should try some spelling variations:
cao viet » dao viet, co viet, ca viet
sach ty » sach tu, sach thu, xach tay
hieu va » lieu va, hieu qua
hanh di » hanh vi, hanh de, hang di
va cau » van cau, va cac, va dau
xuc va » tuc va, luc va, xac va
di cao » di vao, do cao, di cau
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 ty) or (sach y)) nang x hoi. hieu va cau ((xuc va) or (duc va)) hanh di cao viet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: te ((sach ty) OR (sach y)) nang x hoi. hieu va cau ((xuc va) OR (duc va)) hanh di cao viet.
• Adding a wildcard symbol may retrieve word variants: te ((sach ty) or (sach y)) nang x hoi. hieu va cau ((xuc va) or (duc va)) hanh di cao viet*.