Perhaps you should try some spelling variations:
trinh vi » trinh va, trinh ve, trinh viet
su sach » so sach, vu sach
hieu ve » hieu va, hieu van
cac bac » cac ban, cac cach, sach bac
tinh vi » tinh voi, tinh va, dinh vi
y nang » ky nang, ly nang, v nang
x hoi » xa hoi, o hoi, x ho
thiet » thieu

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