Perhaps you should try some spelling variations:
dua tren » dung tren
van hanh » van thanh, ban hanh, van anh
tu sach » thu sach, te sach, tu cach
duc van » duc va, duc tan, duc manh
cam duc » cam xuc, cao duc, pham duc
qua cam » qua cham, qua cac, qua ca
tang xa » trang xa, tang ma, lang xa
ty tang » tay tang, ty xang, ty hang
su sach » so sach, vu sach
cuu tre » cua tre, cau tren, cau treo

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 (su sach)) ty tang xa hoi. hieu qua cam duc van hanh vi ((dua tren) or (cuu tre))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((tu sach) OR (su sach)) ty tang xa hoi. hieu qua cam duc van hanh vi ((dua tren) OR (cuu tre)).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((tu sach) OR (su sach)) ty tang xa hoi. hieu qua cam duc van hanh vi ((dua tren) or (cuu tre))".
• Adding a wildcard symbol may retrieve word variants: ((tu sach) OR (su sach)) ty tang xa hoi. hieu qua cam duc van hanh vi ((dua tren) or (cuu tre))*.