Perhaps you should try some spelling variations:
tu sach » thu sach, su sach, te sach
hieu va » lieu va, hieu qua
nuoc ca » nuoc cua, nuoc cap, nuoc va
dao hai » dao thai, do hai, dao bai
dai hai » dai han, dai hoi, dai tai
cua tre » cua te, cuu tre, cua triet
y lang » _ lang, tay lang, yen lang
o lang » hoa lang, hoi lang
va hoc » van hoc

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 ((y lang) OR (o lang)) xa hoi. hieu va hoc nuoc ca ((dao hai) or (dai hai)) cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ((y lang) OR (o lang)) xa hoi. hieu va hoc nuoc ca ((dao hai) OR (dai hai)) cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach ((y lang) OR (o lang)) xa hoi. hieu va hoc nuoc ca ((dao hai) or (dai hai)) cua tre".
• Adding a wildcard symbol may retrieve word variants: tu sach ((y lang) OR (o lang)) xa hoi. hieu va hoc nuoc ca ((dao hai) or (dai hai)) cua tre*.