Perhaps you should try some spelling variations:
hieu va » lieu va, hieu qua
va giao » van giao, va giai, va gia
va hanh » van hanh, va thanh, va danh
dai cuu » dai cua, dai huu
cuu tre » cua tre, cau tren, cau treo
tu sac » tu sach, tu cac, tu san
sac ky » cac ky, sai ky
o hoi » co hoi, o hoc, o hoa
o hai » co hai, so hai, o lai

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

• Performing a fuzzy search may retrieve terms with similar spellings: tu sac ky nang ((o hoi) OR (o hai)). hieu va giao duc ((va hanh) or (may tinh)) dai cuu tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sac ky nang ((o hoi) OR (o hai)). hieu va giao duc ((va hanh) OR (may tinh)) dai cuu tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sac ky nang ((o hoi) OR (o hai)). hieu va giao duc ((va hanh) or (may tinh)) dai cuu tre".
• Adding a wildcard symbol may retrieve word variants: tu sac ky nang ((o hoi) OR (o hai)). hieu va giao duc ((va hanh) or (may tinh)) dai cuu tre*.