Perhaps you should try some spelling variations:
sach nuoc » sach duoc, cac nuoc, bach tuoc
cau treo » cau theo, cau tren, cau triet
hanh tai » thanh tai, hang tai, han tai
cua tre » cua te, cuu tre, cua triet
va hanh » van hanh, va thanh, va danh
tu sach » thu sach, su sach, te sach
sach ky » sac ky, sach y, sach ty
hieu va » lieu va, hieu qua
va sach » van sach, va cach, a sach
o hoi » co hoi, o hoc, o hai
x hoi » xa hoi, x ho, 5 hoi

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 ky nang ((x hoi) OR (o hoi)). hieu va sach nuoc va hanh tai ((cua tre) or (cau treo))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ky nang ((x hoi) OR (o hoi)). hieu va sach nuoc va hanh tai ((cua tre) OR (cau treo)).
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach ky nang ((x hoi) OR (o hoi)). hieu va sach nuoc va hanh tai ((cua tre) or (cau treo))".
• Adding a wildcard symbol may retrieve word variants: tu sach ky nang ((x hoi) OR (o hoi)). hieu va sach nuoc va hanh tai ((cua tre) or (cau treo))*.