Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
cac nuoc » cap nuoc, hoc nuoc, dat nuoc
hieu ve » hieu va, hieu van
ky dang » ky nang, ky danh
ky sang » ky nang, ky tang, duy sang
ma hoi » mai hoi, xa hoi, ma hoa
ve cac » va cac, vien cac
va dao » ca dao
vi cau » va cau, di cau, viet cau
ve cau » ke cau, va cau, le cau

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 ((ky sang) or (ky dang)) ma hoi. hieu ve cac nuoc va dao ((vi cau) OR (ve cau)) tao~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach ((ky sang) OR (ky dang)) ma hoi. hieu ve cac nuoc va dao ((vi cau) OR (ve cau)) tao.
• The words AND, OR and NOT may confuse the search; try adding quotes: "toc sach ((ky sang) or (ky dang)) ma hoi. hieu ve cac nuoc va dao ((vi cau) OR (ve cau)) tao".
• Adding a wildcard symbol may retrieve word variants: toc sach ((ky sang) or (ky dang)) ma hoi. hieu ve cac nuoc va dao ((vi cau) OR (ve cau)) tao*.