Perhaps you should try some spelling variations:
trinh tai » trinh toan, trinh tu, trinh han
trinh dai » trinh di, trinh da, trinh dan
cac duc » cac du, cao duc, cac dac
sach tu » sach thu, sach ty, sach uu
cach tu » cach thuc
cua tre » cua te, cuu tre, cua triet
hang o » hang do, hang o2, hoang o
o hoi » co hoi, o hoc, o hai

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

• Performing a fuzzy search may retrieve terms with similar spellings: te ((sach tu) or (cach tu)) hang o hoi. lieu va cac duc va ((trinh dai) OR (trinh tai)) cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: te ((sach tu) OR (cach tu)) hang o hoi. lieu va cac duc va ((trinh dai) OR (trinh tai)) cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "te ((sach tu) or (cach tu)) hang o hoi. lieu va cac duc va ((trinh dai) OR (trinh tai)) cua tre".
• Adding a wildcard symbol may retrieve word variants: te ((sach tu) or (cach tu)) hang o hoi. lieu va cac duc va ((trinh dai) OR (trinh tai)) cua tre*.