Perhaps you should try some spelling variations:
van hanh » van thanh, ban hanh, van anh
tu sach » thu sach, su sach, te sach
cua tre » cua te, cuu tre, cua triet
duc van » duc va, duc tan, duc manh
cam duc » cam xuc, cao duc, pham duc
cu tren » tu tren, dua tren
hieu ve » hieu va, hieu van
nang ro » nang co, nang ho, nang ra
nang o » nang co, nang ho, nang x
ve cam » ve cham, ve cac, va cam

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 y ((nang o) or (nang ro)) hoi. hieu ve cam duc van hanh vi ((cua tre) or (cu tren))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach y ((nang o) OR (nang ro)) hoi. hieu ve cam duc van hanh vi ((cua tre) OR (cu tren)).
• Adding a wildcard symbol may retrieve word variants: tu sach y ((nang o) or (nang ro)) hoi. hieu ve cam duc van hanh vi ((cua tre) or (cu tren))*.