Perhaps you should try some spelling variations:
dau tren » dau tien, dat tren, dau tieng
tu sach » thu sach, su sach, te sach
so sach » so sanh, bo sach, co sach
cao hoi » cau hoi, co hoi, cao hoc
hieu ve » hieu va, hieu van
cam tu » cam thu, dam tu, tam tu
nam tu » nam thu, nam thuc
va dan » ca dan, va dao, va dau
ca dau » ca dao, ca dan, va dau

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

• Performing a fuzzy search may retrieve terms with similar spellings: ((tu sach) or (so sach)) ky nang cao hoi. hieu ve ((cam tu) OR (nam tu)) va dan ca dau tren~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((tu sach) OR (so sach)) ky nang cao hoi. hieu ve ((cam tu) OR (nam tu)) va dan ca dau tren.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((tu sach) or (so sach)) ky nang cao hoi. hieu ve ((cam tu) OR (nam tu)) va dan ca dau tren".
• Adding a wildcard symbol may retrieve word variants: ((tu sach) or (so sach)) ky nang cao hoi. hieu ve ((cam tu) OR (nam tu)) va dan ca dau tren*.