Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
hac truc » hoc truc, hang truc, sach truc
hieu van » hieu va, thien van, lieu va
cau tren » cu tren, dau tren, ca tren
sach ty » sach y, sach tu, sach thu
ty nang » ky nang, ty xang, ty hang
truc va » thuc va, thuc vat, trung va
va danh » va dinh, va dan, va hanh
danh vi » hanh vi, dinh vi, danh di
cuu tre » cua tre, cau treo
van hac » van hoc, van ha, van hai
o hoi » co hoi, o hoc, o hai
x hoi » xa hoi, x ho, 5 hoi

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 nang ((x hoi) OR (o hoi)). hieu van hac truc va danh vi ((cuu tre) or (cau tren))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach ty nang ((x hoi) OR (o hoi)). hieu van hac truc va danh vi ((cuu tre) OR (cau tren)).
• The words AND, OR and NOT may confuse the search; try adding quotes: "toc sach ty nang ((x hoi) OR (o hoi)). hieu van hac truc va danh vi ((cuu tre) or (cau tren))".
• Adding a wildcard symbol may retrieve word variants: toc sach ty nang ((x hoi) OR (o hoi)). hieu van hac truc va danh vi ((cuu tre) or (cau tren))*.