Perhaps you should try some spelling variations:
hieu van » hieu va, thien van, lieu va
kinh vai » kinh hai, kinh va, kinh van
cau tren » cu tren, dau tren, ca tren
tu sach » thu sach, su sach, te sach
cao hoi » cau hoi, co hoi, cao hoc
van cau » van dau, van hau, van chat
cau duc » cao duc, cau luc, chu duc
va kinh » va tinh, qua kinh
cuu tre » cua tre, cau treo

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 (thu hoach)) ky nang cao hoi. hieu van cau duc va kinh vai ((cuu tre) OR (cau tren))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((tu sach) OR (thu hoach)) ky nang cao hoi. hieu van cau duc va kinh vai ((cuu tre) OR (cau tren)).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((tu sach) or (thu hoach)) ky nang cao hoi. hieu van cau duc va kinh vai ((cuu tre) OR (cau tren))".
• Adding a wildcard symbol may retrieve word variants: ((tu sach) or (thu hoach)) ky nang cao hoi. hieu van cau duc va kinh vai ((cuu tre) OR (cau tren))*.