Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
sach thi » sach thu, sach tai, sach thieu
van hanh » van thanh, ban hanh, van anh
cua viet » ca viet, hoa viet, cua vat
hanh cat » hanh cac, hanh cham, hanh luat
thi hanh » thi thanh
hieu va » lieu va, hieu qua
cac tuc » cac tu, cac tac, cac nuoc
cat hoi » cau hoi, sat hoi, chat hoa
cac toc » cac toi, cac nuoc, cac thoi
xa hanh » xa thanh, xa khanh, va hanh

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 thi hanh cat hoi. hieu va ((cac tuc) or (cac toc)) ((xa hanh) or (van hanh)) dai cua viet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach thi hanh cat hoi. hieu va ((cac tuc) OR (cac toc)) ((xa hanh) OR (van hanh)) dai cua viet.
• Adding a wildcard symbol may retrieve word variants: toc sach thi hanh cat hoi. hieu va ((cac tuc) or (cac toc)) ((xa hanh) or (van hanh)) dai cua viet*.