Perhaps you should try some spelling variations:
vanh dai » van dai, vanh tai, lanh dao
hanh dai » hanh tai, hanh dao, thanh dat
cac nuoc » cap nuoc, hoc nuoc, dat nuoc
cua tre » cua te, cuu tre, cua triet
hieu ve » hieu va, hieu van
dai hai » dai han, dai tai, dai thao
dai hoi » dai hoc, dai moi
sai ky » sac ky
ve cac » va cac, vien cac
su sai » su tai, su hai, su dai

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

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