Perhaps you should try some spelling variations:
duc tren » duoc tren, dua tren, duc tien
toc sach » hoc sach, doc sach, thuoc sach
van nang » van quang, van ban, van dong
hieu van » hieu va, thien van, lieu va
hang di » hang doi, hang vi, hang dien
va hang » van hang, va nang, va lang
tu sach » thu sach, su sach, te sach
ky tang » ky nang, ky dang, kho tang
ky lang » ky nang, ky dang, tay lang
luc va » duc va, tuc va, loc va
di duc » do duc, di du, oi duc

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) or (toc sach)) ((ky lang) OR (ky tang)) xa hoi. hieu van nang luc va hang di duc tren~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((tu sach) OR (toc sach)) ((ky lang) OR (ky tang)) xa hoi. hieu van nang luc va hang di duc tren.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((tu sach) or (toc sach)) ((ky lang) OR (ky tang)) xa hoi. hieu van nang luc va hang di duc tren".
• Adding a wildcard symbol may retrieve word variants: ((tu sach) or (toc sach)) ((ky lang) OR (ky tang)) xa hoi. hieu van nang luc va hang di duc tren*.