Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
hoc cac » hoc cao
cao hoi » cau hoi, co hoi, cao hoc
qua dam » cua dam, qua da, dua dam
va dinh » van dinh, va kinh, va tinh
dinh ve » dinh ket, dinh van
su viet » so viet
dam tu » nam tu, cam tu, tam tu
ve su » va su

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) or (hoc cac)) ky nang cao hoi. hieu qua dam tu va dinh ve su viet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((toc sach) OR (hoc cac)) ky nang cao hoi. hieu qua dam tu va dinh ve su viet.
• Adding a wildcard symbol may retrieve word variants: ((toc sach) or (hoc cac)) ky nang cao hoi. hieu qua dam tu va dinh ve su viet*.