Perhaps you should try some spelling variations:
vat hanh » vat thanh, van hanh, va hanh
pham duy » pham duc
cua tre » cua te, cuu tre, cua triet
va pham » van pham, va phat, va phap
hieu va » lieu va, hieu qua
vi cua » vai cua, di cua
sac ky » cac ky
ha hoi » hoa hoi, ha noi, va hoi

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

• Performing a fuzzy search may retrieve terms with similar spellings: su ((sac ky) or (sai ky)) lang ((ha hoi) or (xa hoi)). hieu va pham duy vat hanh vi cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su ((sac ky) OR (sai ky)) lang ((ha hoi) OR (xa hoi)). hieu va pham duy vat hanh vi cua tre.
• Adding a wildcard symbol may retrieve word variants: su ((sac ky) or (sai ky)) lang ((ha hoi) or (xa hoi)). hieu va pham duy vat hanh vi cua tre*.