Perhaps you should try some spelling variations:
cac thuc » cach thuc, cac thu, can thuc
tu sach » thu sach, su sach, te sach
doan vi » doan va, don vi, doan thi
thuc va » thuc vat, thuc dan, thuc day
hieu ve » hieu va, hieu van
cua tre » cua te, cuu tre, cua triet
ty hang » ly hang, ty xang, thi hang
ty lang » tay lang, ty xang, tu lang
dan va » doan va, dan ca, ban va
ve cac » va cac, vien cac

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

• Performing a fuzzy search may retrieve terms with similar spellings: tu sach ((ty lang) OR (ty hang)) xa hoi. hieu ve cac thuc va ((dan va) or (doan vi)) cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ((ty lang) OR (ty hang)) xa hoi. hieu ve cac thuc va ((dan va) OR (doan vi)) cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach ((ty lang) OR (ty hang)) xa hoi. hieu ve cac thuc va ((dan va) or (doan vi)) cua tre".
• Adding a wildcard symbol may retrieve word variants: tu sach ((ty lang) OR (ty hang)) xa hoi. hieu ve cac thuc va ((dan va) or (doan vi)) cua tre*.