Perhaps you should try some spelling variations:
doc sac » doc sach, dac sac, hoc sach
hieu ve » hieu va, hieu van
cac dac » cac dan, cac dai, cac bac
va danh » va dinh, va dan, va hanh
danh ki » danh di, danh kien, danh gia
su hien » su kien, su tien, thu hien
sac ky » cac ky, sai ky
ma hoi » mai hoi, ma hoa, me hoi
ve cac » va cac, vien cac
dac va » duc va, day va, dat va
ki su » ky su

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

• Performing a fuzzy search may retrieve terms with similar spellings: doc sac ky nang ((ma hoi) or (xa hoi)). hieu ve cac dac va danh ki su hien~.
• If you are trying to use Boolean operators, they must be ALL CAPS: doc sac ky nang ((ma hoi) OR (xa hoi)). hieu ve cac dac va danh ki su hien.
• Adding a wildcard symbol may retrieve word variants: doc sac ky nang ((ma hoi) or (xa hoi)). hieu ve cac dac va danh ki su hien*.