Perhaps you should try some spelling variations:
vanh dai » van dai, vanh tai, lanh dao
hanh dai » hanh tai, hanh dao, thanh dat
su sach » so sach, vu sach
duc van » duc va, duc tan, duc manh
dau duc » dao duc, dang duc, dau nuoc
cua tre » cua te, cuu tre, cua triet
hieu va » lieu va, hieu qua
nang ma » tang ma, sang ma, nang cao
nang xa » nang x, lang xa, mang xa
va dau » va dao

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

• Performing a fuzzy search may retrieve terms with similar spellings: su sach y ((nang xa) or (nang ma)) hoi. hieu va dau duc van ((hanh dai) OR (vanh dai)) cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su sach y ((nang xa) OR (nang ma)) hoi. hieu va dau duc van ((hanh dai) OR (vanh dai)) cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "su sach y ((nang xa) or (nang ma)) hoi. hieu va dau duc van ((hanh dai) OR (vanh dai)) cua tre".
• Adding a wildcard symbol may retrieve word variants: su sach y ((nang xa) or (nang ma)) hoi. hieu va dau duc van ((hanh dai) OR (vanh dai)) cua tre*.