Perhaps you should try some spelling variations:
van thiet » va thiet, dan thiet, can thiet
su sach » so sach, vu sach
sach ly » sach y, sach lo, sach ty
ly nang » ky nang, ly hang, ly vang
van cac » van hac, van cau, dan cac
van bac » van ban, van bao, van hac
tinh vi » trinh vi, tinh voi, tinh va
bac va » ban va, bao va, tac va
x hoi » xa hoi, o hoi, x ho

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 ly nang x hoi. hieu ((van cac) or (van bac)) ((bac va) OR (bac ha)) tinh vi van thiet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su sach ly nang x hoi. hieu ((van cac) OR (van bac)) ((bac va) OR (bac ha)) tinh vi van thiet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "su sach ly nang x hoi. hieu ((van cac) or (van bac)) ((bac va) OR (bac ha)) tinh vi van thiet".
• Adding a wildcard symbol may retrieve word variants: su sach ly nang x hoi. hieu ((van cac) or (van bac)) ((bac va) OR (bac ha)) tinh vi van thiet*.