Perhaps you should try some spelling variations:
hieu van » thien van, lieu va, hieu ve
van hanh » van thanh, ban hanh, van anh
cua viet » ca viet, hoa viet, cua vat
tu sach » thu sach, te sach, tu cach
su sach » so sach, vu sach
hieu va » lieu va, hieu qua
bo van » vo van, so van, do van
vi cua » vai cua, di 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: ((tu sach) OR (su sach)) ky nang x hoi. ((hieu van) or (hieu va)) bac bo van hanh vi cua viet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((tu sach) OR (su sach)) ky nang x hoi. ((hieu van) OR (hieu va)) bac bo van hanh vi cua viet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((tu sach) OR (su sach)) ky nang x hoi. ((hieu van) or (hieu va)) bac bo van hanh vi cua viet".
• Adding a wildcard symbol may retrieve word variants: ((tu sach) OR (su sach)) ky nang x hoi. ((hieu van) or (hieu va)) bac bo van hanh vi cua viet*.