Perhaps you should try some spelling variations:
duong truong » duong trong, truong trung, tang truong
tranh duong » trinh duong, thanh duong, tuan duong
truong long » trong long, trung long, truong cong
hieu cac » hieu luc, hieu va, hieu van
long van » luong van, song van, lang van
ban tap » bai tap, han tap, ban tai

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

• Performing a fuzzy search may retrieve terms with similar spellings: hoc ((hieu cac) or (hieu qua)) - canh tranh duong truong long van ban tap~.
• If you are trying to use Boolean operators, they must be ALL CAPS: hoc ((hieu cac) OR (hieu qua)) - canh tranh duong truong long van ban tap*.