Perhaps you should try some spelling variations:
vu khach » vu khanh, vu khac, vay khach
hieu van » hieu va, thien van, lieu va
su sach » so sach, vu sach
truc va » thuc va, thuc vat, trung va
dan vat » dang vat, van vat, dan va
dan vai » dan va, dan tai, den vai
van cau » van dau, van hau, van chat
nang ma » tang ma, sang ma, nang cao
cua tre » cua te, cuu tre, cua triet
ma hoi » mai hoi, xa hoi, ma hoa

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

• Performing a fuzzy search may retrieve terms with similar spellings: ((su sach) or (vu khach)) ky nang ma hoi. hieu van cau truc va ((dan vai) OR (dan vat)) cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((su sach) OR (vu khach)) ky nang ma hoi. hieu van cau truc va ((dan vai) OR (dan vat)) cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((su sach) or (vu khach)) ky nang ma hoi. hieu van cau truc va ((dan vai) OR (dan vat)) cua tre".
• Adding a wildcard symbol may retrieve word variants: ((su sach) or (vu khach)) ky nang ma hoi. hieu van cau truc va ((dan vai) OR (dan vat)) cua tre*.