Perhaps you should try some spelling variations:
dau tren » dau tien, dat tren, dau tieng
cach dau » sach dau, mach dau, cac dan
cam tuc » cam xuc, cam tu, nam thuc
sach ky » sac ky, sach y, sach ty
hieu ve » hieu va, hieu van
tu sach » thu sach, su sach, te sach
cao hoc » co hoc, cho hoc, chat hoc
va dan » va dao, va dau, va dap
ca dan » cac dan, ca dao
co hoi » co hoc, co loi
ve cam » ve cham, ve cac, va cam

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