Perhaps you should try some spelling variations:
nang doc » nang luc
hieu ve » hieu va, hieu van
sach ky » sac ky, sach ty, sach kem
nang ho » nang hoc, nang co, tang ho
cua tre » cua te, cuu tre, cua triet
ve cac » va cac, vien cac
cac tu » cac thu, cach tu, cac du
vi cua » vai cua, di cua
va do » va dao, va doc, va co
do vi » don vi, doc vi, do voi

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) or (sach y)) ((nang ho) or (nang doc)) hoi. hieu ve cac tu va do vi cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu ((sach ky) OR (sach y)) ((nang ho) OR (nang doc)) hoi. hieu ve cac tu va do vi cua tre.
• Adding a wildcard symbol may retrieve word variants: tu ((sach ky) or (sach y)) ((nang ho) or (nang doc)) hoi. hieu ve cac tu va do vi cua tre*.