Perhaps you should try some spelling variations:
dang hanh » dang thanh, ban hanh, dang van
dan hanh » dan khanh, dan thanh, ban hanh
cua viet » ca viet, hoa viet, cua vat
so sach » so sanh, bo sach, co sach
qua cac » cua cac
cac hoc » cach hoc, cac hop, bac hoc
v nang » va nang, vu nang, van nang
di cua » dai cua, doi cua, de cua

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

• Performing a fuzzy search may retrieve terms with similar spellings: so sach ((v nang) or (van ban)) xa hoi. hieu qua cac hoc ((dan hanh) OR (dang hanh)) di cua viet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: so sach ((v nang) OR (van ban)) xa hoi. hieu qua cac hoc ((dan hanh) OR (dang hanh)) di cua viet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "so sach ((v nang) or (van ban)) xa hoi. hieu qua cac hoc ((dan hanh) OR (dang hanh)) di cua viet".
• Adding a wildcard symbol may retrieve word variants: so sach ((v nang) or (van ban)) xa hoi. hieu qua cac hoc ((dan hanh) OR (dang hanh)) di cua viet*.