Perhaps you should try some spelling variations:
hieu van » hieu va, thien van, lieu va
sach ty » sach y, sach tu, sach thu
doi cua » dai cua, hoi cua
va hanh » van hanh, va thanh, va danh
cac bac » cac bai, cac ban, cac cach
tu sach » thu sach, su sach, te sach
cac duc » cac du, cao duc, cac dac
cao hoi » cau hoi, co hoi, cao hoc
ty nang » ky nang, ty xang, ty hang
di cua » dai cua, de cua, do cua

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 ty nang cao hoi. hieu van ((cac duc) or (cac bac)) va hanh ((di cua) OR (doi cua)) viet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ty nang cao hoi. hieu van ((cac duc) OR (cac bac)) va hanh ((di cua) OR (doi cua)) viet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach ty nang cao hoi. hieu van ((cac duc) or (cac bac)) va hanh ((di cua) OR (doi cua)) viet".
• Adding a wildcard symbol may retrieve word variants: tu sach ty nang cao hoi. hieu van ((cac duc) or (cac bac)) va hanh ((di cua) OR (doi cua)) viet*.