Perhaps you should try some spelling variations:
hanh via » hanh vi, anh va, hanh ve
su sach » so sach, vu sach
hanh va » hang va, hanh vi
sach ky » sac ky, sach y, sach ty
qua bac » qua ban, qua cac, cua bac
mai hoi » mai khoi, dai hoi, lai hoi
cua tre » cua te, cuu tre, cua triet
ma hoi » xa hoi, ma hoa, me hoi
bo va » bao va, do va, so va

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 ky nang ((ma hoi) or (mai hoi)). hieu qua bac bo va ((hanh via) OR (hanh va)) cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su sach ky nang ((ma hoi) OR (mai hoi)). hieu qua bac bo va ((hanh via) OR (hanh va)) cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "su sach ky nang ((ma hoi) or (mai hoi)). hieu qua bac bo va ((hanh via) OR (hanh va)) cua tre".
• Adding a wildcard symbol may retrieve word variants: su sach ky nang ((ma hoi) or (mai hoi)). hieu qua bac bo va ((hanh via) OR (hanh va)) cua tre*.