Perhaps you should try some spelling variations:
dau tren » dau tien, dat tren, dau tieng
hieu van » hieu va, thien van, lieu va
cach dau » sach dau, mach dau, cac dan
dan cach » dan cac, dan canh, nhan cach
cam truc » cau truc, nam truc, lam truoc
truc va » thuc va, thuc vat, trung va
tu sach » thu sach, su sach, te sach
sach ky » sac ky, sach y, sach ty
hieu ve » hieu va
cao hoc » co hoc, cho hoc, chat hoc
va dan » ca dan, va dao, va dau
co hoi » co hoc, co loi

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) or (hieu van)) cam truc va 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) OR (hieu van)) cam truc va dan cach dau tren.
• Adding a wildcard symbol may retrieve word variants: tu sach ky nang ((co hoi) or (cao hoc)). ((hieu ve) or (hieu van)) cam truc va dan cach dau tren*.