Perhaps you should try some spelling variations:
thien van » thi van
toc sach » hoc sach, doc sach, thuoc sach
sach ty » sach y, sach tu, sach thu
ty hang » ly hang, ty xang, thi hang
van cac » van hac, van cau, van bac
cua tre » cua te, cuu tre, cua triet
hang o » hang do, hang o2, hoang o
bo van » vo van, do van, ho van
so van » su van, vo van
vi cua » vai cua, di cua
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: toc sach ty hang o hoi. thien van cac ((bo van) or (so van)) hanh vi cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach ty hang o hoi. thien van cac ((bo van) OR (so van)) hanh vi cua tre.
• Adding a wildcard symbol may retrieve word variants: toc sach ty hang o hoi. thien van cac ((bo van) or (so van)) hanh vi cua tre*.