Perhaps you should try some spelling variations:
hieu vien » hieu hien, hieu viec, thieu nien
cac nuoc » cap nuoc, hoc nuoc, dat nuoc
ban hanh » ban hang
so sach » so sanh, bo sach, co sach
su viet » so viet
hanh di » hanh vi, hanh de, hang di
ca viet » va viet, co viet, hoa viet
cac toc » cac toi, cac thoi
y nang » ky nang, ly nang, v nang
nang o » nang co, nang ho, nang ro
o hoi » co hoi, o hoc, o hai

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: so sach y nang o hoi. hieu vien ((cac toc) or (cac nuoc)) ban hanh di ((su viet) or (ca viet))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: so sach y nang o hoi. hieu vien ((cac toc) OR (cac nuoc)) ban hanh di ((su viet) OR (ca viet)).
• Adding a wildcard symbol may retrieve word variants: so sach y nang o hoi. hieu vien ((cac toc) or (cac nuoc)) ban hanh di ((su viet) or (ca viet))*.