Perhaps you should try some spelling variations:
sach ky » sach y, sach ty, sach kem
hieu ve » hieu va, hieu van
va hanh » van hanh, va thanh, va danh
cua tre » cua te, cua triet, dua tren
cuu tre » cau tren, cau treo
sac ky » cac ky, sai ky
ve bac » ve bao, ve cac, ve ban
x hoi » xa hoi, o hoi, x ho
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) or (sac ky)) nang x hoi. hieu ve bac bo va hanh vi ((cua tre) OR (cuu tre))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su ((sach ky) OR (sac ky)) nang x hoi. hieu ve bac bo va hanh vi ((cua tre) OR (cuu tre)).
• The words AND, OR and NOT may confuse the search; try adding quotes: "su ((sach ky) or (sac ky)) nang x hoi. hieu ve bac bo va hanh vi ((cua tre) OR (cuu tre))".
• Adding a wildcard symbol may retrieve word variants: su ((sach ky) or (sac ky)) nang x hoi. hieu ve bac bo va hanh vi ((cua tre) OR (cuu tre))*.