Perhaps you should try some spelling variations:
qua tham » qua cham, qua than, qua thanh
thanh vi » hanh vi, thanh va, thanh ve
hoc bai » hoc dai, hoc giai
hoc ban » hoc bang, hoc dan, hoc can
cua tre » cua te, cuu tre, cua triet
tang ha » lang ha, trung ha, tang van
tang ma » mang may, tang van
vi cua » vai cua, di cua
te cac » tu cac, ve cac, te cao

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

• Performing a fuzzy search may retrieve terms with similar spellings: te cac ky ((tang ha) or (tang ma)) hoi. hieu qua tham ((hoc ban) OR (hoc bai)) thanh vi cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: te cac ky ((tang ha) OR (tang ma)) hoi. hieu qua tham ((hoc ban) OR (hoc bai)) thanh vi cua tre*.
• The words AND, OR and NOT may confuse the search; try adding quotes: "te cac ky ((tang ha) or (tang ma)) hoi. hieu qua tham ((hoc ban) OR (hoc bai)) thanh vi cua tre*".