Perhaps you should try some spelling variations:
doc sach » toc sach, nuoc sach, dac sac
hang tai » hang va, dung tai
hanh tai » thanh tai, han tai, hinh tai
nuoc van » nuoc va, nuoc san, luoc van
cac nuoc » cap nuoc, hoc nuoc, dat nuoc
hoc sach » hoc sinh, hoc cac, hoc anh
hieu va » lieu va, hieu qua
cua tre » cua te, cuu tre, cua triet
nang o » nang co, nang ho, nang ro
o hoi » co hoi, o hoc, o hai

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

• Performing a fuzzy search may retrieve terms with similar spellings: ((doc sach) or (hoc sach)) ky nang o hoi. hieu va cac nuoc van ((hanh tai) or (hang tai)) cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((doc sach) OR (hoc sach)) ky nang o hoi. hieu va cac nuoc van ((hanh tai) OR (hang tai)) cua tre.
• Adding a wildcard symbol may retrieve word variants: ((doc sach) or (hoc sach)) ky nang o hoi. hieu va cac nuoc van ((hanh tai) or (hang tai)) cua tre*.