Perhaps you should try some spelling variations:
vu khach » vu khanh, vu khac, vay khach
hieu van » hieu va, thien van, lieu va
cac nuoc » cap nuoc, hoc nuoc, dat nuoc
va thanh » gia thanh, ban thanh, va tinh
ky lang » ky nang, ky dang, tay lang
ky tang » ky nang, ky dang, kho tang
van cac » van hac, van cau, van bac
va hanh » van hanh, va danh, ban hanh
cua tre » cua te, cuu tre, cua triet

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

• Performing a fuzzy search may retrieve terms with similar spellings: vu khach ((ky lang) or (ky tang)) xa hoi. hieu van cac nuoc ((va hanh) OR (va thanh)) dai cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: vu khach ((ky lang) OR (ky tang)) xa hoi. hieu van cac nuoc ((va hanh) OR (va thanh)) dai cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "vu khach ((ky lang) or (ky tang)) xa hoi. hieu van cac nuoc ((va hanh) OR (va thanh)) dai cua tre".
• Adding a wildcard symbol may retrieve word variants: vu khach ((ky lang) or (ky tang)) xa hoi. hieu van cac nuoc ((va hanh) OR (va thanh)) dai cua tre*.