Perhaps you should try some spelling variations:
vanh dai » van dai, vanh tai, lanh dao
hanh dai » hanh tai, hanh dao, thanh dat
cua tre » cua te, cuu tre, cua triet
duc ban » duc tan, duc van, dua ban
ve pham » vi pham, v pham, ve phan
hieu ve » hieu va, hieu van
tang ma » mang may, tang van
nang xa » nang x, lang xa, nang ma
sac ky » cac ky, sai ky
su sac » su sach, su cac, su xac

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 ((nang xa) or (tang ma)) hoi. hieu ve pham duc ban ((hanh dai) OR (vanh dai)) cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su sac ky ((nang xa) OR (tang ma)) hoi. hieu ve pham duc ban ((hanh dai) OR (vanh dai)) cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "su sac ky ((nang xa) or (tang ma)) hoi. hieu ve pham duc ban ((hanh dai) OR (vanh dai)) cua tre".
• Adding a wildcard symbol may retrieve word variants: su sac ky ((nang xa) or (tang ma)) hoi. hieu ve pham duc ban ((hanh dai) OR (vanh dai)) cua tre*.