Perhaps you should try some spelling variations:
vat hanh » vat thanh, van hanh, va hanh
truc vat » thuc vat, truc va, truc van
tu sach » thu sach, su sach, tu cach
hieu ve » hieu va, hieu van
cua tre » cua te, cuu tre, cua triet
ky lang » ky nang, ky dang, ky tang
te sach » toc sach
ha hoi » hoa hoi, ha noi, va hoi
ve cau » ke cau, va cau, ve cac
vi cua » vai cua, di cua

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 (te sach)) ky lang ((ha hoi) OR (xa hoi)). hieu ve cau truc vat hanh vi cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((tu sach) OR (te sach)) ky lang ((ha hoi) OR (xa hoi)). hieu ve cau truc vat hanh vi cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((tu sach) or (te sach)) ky lang ((ha hoi) OR (xa hoi)). hieu ve cau truc vat hanh vi cua tre".
• Adding a wildcard symbol may retrieve word variants: ((tu sach) or (te sach)) ky lang ((ha hoi) OR (xa hoi)). hieu ve cau truc vat hanh vi cua tre*.