Perhaps you should try some spelling variations:
khai dua » khi dua, khai quat, khai tuan
dua tren » dung tren
su sach » vu sach
so sach » so sanh, bo sach, co sach
cao hoi » cau hoi, co hoi, cao hoc
y nang » ky nang, ly nang, v nang
va cau » van cau, va cac, va dau
va dan » va dao, va dau, va dap
ca dan » cac dan, ca dao

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

• Performing a fuzzy search may retrieve terms with similar spellings: ((su sach) or (so sach)) y nang cao hoi. lieu va cau truc ((va dan) OR (ca dan)) khai dua tren~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((su sach) OR (so sach)) y nang cao hoi. lieu va cau truc ((va dan) OR (ca dan)) khai dua tren*.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((su sach) or (so sach)) y nang cao hoi. lieu va cau truc ((va dan) OR (ca dan)) khai dua tren*".