It is a tough one.  I think I could make a case for any of the answers.
Since the word illegal appears in the question, if it would be a test question I would say d.  If the manager failed to act he could go to jail and people have gone to prison for these violations.
Next I would say b.  The foremans stake is his job and all that comes with it for his family.  If he does nothing and lets this becomes a major issue for the company they will need a scapegoat and it will prob be him and his job.
I dont think the foreman is an activist but activists brought about the stricts laws on pollution.
Market could be proposed also.  If he lets it go on and really becomes a catastrophe, an agency will shut them down and probably for a long time resulting in no productivity.
I'm sticking with d) legal.  It is a tough question.