Perhaps you should try some spelling variations:
sach tu » sach thu, sach ty, sach uu
cach tu » cach thuc
cao hoi » cau hoi, co hoi, cao hoc
hieu ve » hieu va, hieu van
cac duc » cac du, cao duc, cac dac
va hanh » van hanh, va thanh, va danh
vai cua » dai cua, hai cua, lai cua
ve cac » va cac, vien cac
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: te ((sach tu) or (cach tu)) nang cao hoi. hieu ve cac duc va hanh ((vi cua) OR (vai cua)) tu~.
• If you are trying to use Boolean operators, they must be ALL CAPS: te ((sach tu) OR (cach tu)) nang cao hoi. hieu ve cac duc va hanh ((vi cua) OR (vai cua)) tu.
• The words AND, OR and NOT may confuse the search; try adding quotes: "te ((sach tu) or (cach tu)) nang cao hoi. hieu ve cac duc va hanh ((vi cua) OR (vai cua)) tu".
• Adding a wildcard symbol may retrieve word variants: te ((sach tu) or (cach tu)) nang cao hoi. hieu ve cac duc va hanh ((vi cua) OR (vai cua)) tu*.