Perhaps you should try some spelling variations:
cau tren » cu tren, dau tren, ca tren
nang doc » nang luc
nang hoc » nang luc, dong hoc, hang hoa
sach ky » sac ky, sach y, sach ty
tu sach » thu sach, su sach, te sach
hieu ve » hieu va, hieu van
ve cam » ve cham, ve cac, va cam
va dan » va dao, va dau, va dap
ca dan » cac dan, ca dao
ca cau » cua cau, cac cau, can cau

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