Perhaps you should try some spelling variations:
nhung cong » dung cong, thong cong, hang cong
hieu lang » chieu sang, hieu quang, nhieu tang
nho hieu » nha hieu, nho sieu, nhu hieu
cong bai » cuong bai, cong hai, cung bai
bai toan » bai tap
toan cao » toan ban, toan tap
mang va » mang vua, bang va, mang xa
dang va » dang van, dang vat, dung va

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

• If you are trying to use Boolean operators, they must be ALL CAPS: nho hieu lang - hanh ((((mang va) OR (dang va))) OR (hang va)) nhung cong bai toan cao~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "nho hieu lang - hanh ((((mang va) OR (dang va))) or (hang va)) nhung cong bai toan cao~".
• Adding a wildcard symbol may retrieve word variants: nho hieu lang - hanh ((((mang va) OR (dang va))) or (hang va)) nhung cong bai toan cao*.