Perhaps you should try some spelling variations:
nam trung » nam trong, tai trung, ba trung
cam trung » cam truong, cac trung, cao trung
nang dai » nang dau, nang tai, nang cai
hanh vai » hanh vi, hanh va, hanh tai
lang dai » lang hai, lang mai, lang chai
va hanh » van hanh, va thanh, va danh
so sach » so sanh, bo sach, co sach
va viet » hoa viet, san viet, mai viet
vai va » mai va, dai va, hai va

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 y ((nang dai) or (lang dai)) hoi. hieu qua ((cam trung) or (nam trung)) va hanh vai va viet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: so sach y ((nang dai) OR (lang dai)) hoi. hieu qua ((cam trung) OR (nam trung)) va hanh vai va viet.
• Adding a wildcard symbol may retrieve word variants: so sach y ((nang dai) or (lang dai)) hoi. hieu qua ((cam trung) or (nam trung)) va hanh vai va viet*.