Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
van hanh » van thanh, ban hanh, van anh
dua tren » dung tren
ky lang » ky nang, ky dang, ky tang
lang xa » lang ha, dang xay, lang van
hieu ve » hieu va, hieu van
ve cac » va cac, vien cac
cac tu » cac thu, cach tu, cac du
tu van » tu va
vi dua » vi du, vi dum, vi lua

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: ((te sach) OR (toc sach)) ky lang xa hoi. hieu ve cac tu van hanh vi dua tren~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((te sach) OR (toc sach)) ky lang xa hoi. hieu ve cac tu van hanh vi dua tren".
• Adding a wildcard symbol may retrieve word variants: ((te sach) OR (toc sach)) ky lang xa hoi. hieu ve cac tu van hanh vi dua tren*.