Perhaps you should try some spelling variations:
nhung cong » thong cong, hang cong, nhung don
hien xanh » hien hanh, hien nhanh, chieu xanh
dung cong » dung trong
canh ban » can ban, canh dan, canh van
san toan » van toan, dan toan, manh toan
toan cao » toan ban, toan tap
can van » cac van, can ban, tan van

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

• Performing a fuzzy search may retrieve terms with similar spellings: hoc hien xanh - ((canh ban) or (can van)) quan ((nhung cong) OR (dung cong)) san toan cao~.
• If you are trying to use Boolean operators, they must be ALL CAPS: hoc hien xanh - ((canh ban) OR (can van)) quan ((nhung cong) OR (dung cong)) san toan cao.
• The words AND, OR and NOT may confuse the search; try adding quotes: "hoc hien xanh - ((canh ban) or (can van)) quan ((nhung cong) OR (dung cong)) san toan cao".
• Adding a wildcard symbol may retrieve word variants: hoc hien xanh - ((canh ban) or (can van)) quan ((nhung cong) OR (dung cong)) san toan cao*.