Perhaps you should try some spelling variations:
hoc sach » hoc sinh, hoc cac, hoc anh
hieu va » lieu va, hieu qua
va chat » van chat, va phat, cao chat
doan vi » doan va, don vi, doan thi
cua tre » cua te, cuu tre, cua triet
xuc va » duc va, tuc va, xac va
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: hoc sach ((su dang) or (su dung)) xa hoi. hieu va chat ((xuc va) OR (luc va)) doan vi cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: hoc sach ((su dang) OR (su dung)) xa hoi. hieu va chat ((xuc va) OR (luc va)) doan vi cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "hoc sach ((su dang) or (su dung)) xa hoi. hieu va chat ((xuc va) OR (luc va)) doan vi cua tre".
• Adding a wildcard symbol may retrieve word variants: hoc sach ((su dang) or (su dung)) xa hoi. hieu va chat ((xuc va) OR (luc va)) doan vi cua tre*.