Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
lang hai » lang chai, lang thai, lang ha
hanh ve » hanh vi, hanh va, hanh kem
hoc bai » hoc dai, hoc giai
hoc ban » hoc bang, hoc dan, hoc can
va cham » va chat, va tham
hieu va » lieu va, hieu qua
hai hoi » dai hoi, hai moi, hai hai
ky lang » ky nang, ky dang, ky tang
cua tre » cua te, cuu tre, cua triet
ve cua » le cua, de cua, te cua

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) or (toc sach)) ky lang hai hoi. hieu va cham ((hoc ban) OR (hoc bai)) hanh ve cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((te sach) OR (toc sach)) ky lang hai hoi. hieu va cham ((hoc ban) OR (hoc bai)) hanh ve cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((te sach) or (toc sach)) ky lang hai hoi. hieu va cham ((hoc ban) OR (hoc bai)) hanh ve cua tre".
• Adding a wildcard symbol may retrieve word variants: ((te sach) or (toc sach)) ky lang hai hoi. hieu va cham ((hoc ban) OR (hoc bai)) hanh ve cua tre*.