Perhaps you should try some spelling variations:
hieu van » hieu va, thien van, lieu va
su sach » so sach, vu sach
sach ky » sac ky, sach y, sach ty
cao hoc » co hoc, cho hoc, chat hoc
van cac » van hac, van cau, van bac
cac duc » cac du, cao duc, cac dac
va hanh » van hanh, va thanh, va danh
vai cua » dai cua, hai cua, lai cua
vi cua » di cua

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

• Performing a fuzzy search may retrieve terms with similar spellings: su sach ky nang ((cau hoi) or (cao hoc)). hieu van cac duc va hanh ((vi cua) or (vai cua)) viet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su sach ky nang ((cau hoi) OR (cao hoc)). hieu van cac duc va hanh ((vi cua) OR (vai cua)) viet.
• Adding a wildcard symbol may retrieve word variants: su sach ky nang ((cau hoi) or (cao hoc)). hieu van cac duc va hanh ((vi cua) or (vai cua)) viet*.