Perhaps you should try some spelling variations:
van hanh » van thanh, ban hanh, van anh
sach ky » sac ky, sach ty, sach kem
hieu ve » hieu va, hieu van
cua tre » cua te, cuu tre, cua triet
nang xa » lang xa, nang ma, mang xa
ve cac » va cac, vien cac
vi cua » vai cua, di cua
cac o » cac co, cac bo, cac ho
o van » vo van, so van, do van

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

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