Perhaps you should try some spelling variations:
vai thiet » va thiet, tai thiet, van thiet
hieu cao » chieu cao, hieu cac, hieu ca
tu sach » thu sach, su sach, te sach
sach ky » sac ky, sach y, sach ty
cao hoi » co hoi, cao hoc, tao hoi
xuc van » luc van, vuc van, xuc ban
duc van » duc va, duc tan, duc manh
hanh va » hang va, hanh vi
va vai » va bai, va van, va dai

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