Perhaps you should try some spelling variations:
canh trinh » canh tranh, hanh trinh, canh tinh
nhung cong » dung cong, thong cong, hang cong
hoc thieu » toc thieu
bang cong » dang cong, bang song, hang cong
trinh va » trinh van, trinh vat, trinh ve
tap toan » tap doan, tap quan, bai toan
toan ban » van ban

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: ((hoc thieu) OR (hoc hien)) xanh - canh trinh va ((nhung cong) OR (bang cong)) tap toan ban~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((hoc thieu) OR (hoc hien)) xanh - canh trinh va ((nhung cong) or (bang cong)) tap toan ban~".
• Adding a wildcard symbol may retrieve word variants: ((hoc thieu) OR (hoc hien)) xanh - canh trinh va ((nhung cong) or (bang cong)) tap toan ban*.