Perhaps you should try some spelling variations:
dua tren » dung tren
toc sach » hoc sach, doc sach, thuoc sach
nam thuc » nam thuoc, am thuc, nam thu
nam duc » nam duoc, pham duc, nam buoc
lang di » lang dai, hang di, lang du
va lang » va nang, hoa lang
tu sach » thu sach, su sach, te sach
hieu va » lieu va, hieu qua
lang xa » lang ha, dang xay, lang van
ky lang » ky nang, ky dang, ky tang
di dua » dai dua, di du, de dua

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 xa hoi. hieu va ((nam duc) or (nam thuc)) va lang di dua tren~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((tu sach) OR (toc sach)) ky lang xa hoi. hieu va ((nam duc) OR (nam thuc)) va lang di dua tren.
• Adding a wildcard symbol may retrieve word variants: ((tu sach) or (toc sach)) ky lang xa hoi. hieu va ((nam duc) or (nam thuc)) va lang di dua tren*.