Perhaps you should try some spelling variations:
sach ky » sac ky, sach y, sach kem
tinh vi » trinh vi, tinh voi, tinh va
va tinh » may tinh
qua coc » qua cac, qua co, qua con
hoa hoi » khoa hoi, hoa hoc, hoa doi
cua tre » cua te, cuu tre, cua triet
sach ty » sach y, sach tu, sach thu
ha hoi » ha noi, xa hoi, va hoi
luc va » duc va, tuc va, loc va
vi cua » vai cua, di cua

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 (sach ty)) lang ((ha hoi) OR (hoa hoi)). hieu qua coc luc va tinh vi cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su ((sach ky) OR (sach ty)) lang ((ha hoi) OR (hoa hoi)). hieu qua coc luc va tinh vi cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "su ((sach ky) or (sach ty)) lang ((ha hoi) OR (hoa hoi)). hieu qua coc luc va tinh vi cua tre".
• Adding a wildcard symbol may retrieve word variants: su ((sach ky) or (sach ty)) lang ((ha hoi) OR (hoa hoi)). hieu qua coc luc va tinh vi cua tre*.