Perhaps you should try some spelling variations:
nhung cong » dung cong, thong cong, hang cong
hieu xanh » chieu xanh, hieu manh, hieu nganh
doc hieu » toc thieu, hoc thieu, hoc hien
dung cua » dung cho
cong bai » cuong bai, cong hai, cung bai
bai toan » bai tap
toan ban » van ban

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

• Performing a fuzzy search may retrieve terms with similar spellings: doc hieu xanh - thanh ((dung cua) OR (dung luan)) nhung cong bai toan ban~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "doc hieu xanh - thanh ((dung cua) OR (dung luan)) nhung cong bai toan ban".
• Adding a wildcard symbol may retrieve word variants: doc hieu xanh - thanh ((dung cua) OR (dung luan)) nhung cong bai toan ban*.