Perhaps you should try some spelling variations:
dau tai » dai tai, dat tai, da tai
thuc va » thuc vat, thuc dan, thuc day
sach ky » sach y, sach ty, sach kem
lang xa » lang ha, dang xay, lang van
buu tre » cuu tre
va nam » van nam, ha nam
va nay » va ngay, va cay
sac ky » cac ky, sai ky
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: doc ((sach ky) OR (sac ky)) lang xa hoi. hieu ((va nam) or (va nay)) thuc va dau tai buu tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: doc ((sach ky) OR (sac ky)) lang xa hoi. hieu ((va nam) OR (va nay)) thuc va dau tai buu tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "doc ((sach ky) OR (sac ky)) lang xa hoi. hieu ((va nam) or (va nay)) thuc va dau tai buu tre".
• Adding a wildcard symbol may retrieve word variants: doc ((sach ky) OR (sac ky)) lang xa hoi. hieu ((va nam) or (va nay)) thuc va dau tai buu tre*.