Perhaps you should try some spelling variations:
vu khach » vu khanh, vu khac, vay khach
vu sach » vu bach, su sach
va hanh » van hanh, va thanh, va danh
cua tre » cua te, cuu tre, cua triet
nang o » nang co, nang ho, nang ro
va cam » va cham, va cao, va cai
vi cua » vai cua, di cua
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: ((vu sach) or (vu khach)) ky nang o hoi. hieu ((va cam) OR (va cac)) tu va hanh vi cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((vu sach) OR (vu khach)) ky nang o hoi. hieu ((va cam) OR (va cac)) tu va hanh vi cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((vu sach) or (vu khach)) ky nang o hoi. hieu ((va cam) OR (va cac)) tu va hanh vi cua tre".
• Adding a wildcard symbol may retrieve word variants: ((vu sach) or (vu khach)) ky nang o hoi. hieu ((va cam) OR (va cac)) tu va hanh vi cua tre*.