Hey Nina,
is B wrong because "the more privileged sectors" refers to "working class"?
I'm not sure I understand what that would have to do with answer choice (B). And besides, "privileged sectors" and "working class" are inherently opposites. (B) is wrong because the only thing we know about why the plant shut down is: "...upon the formation of the union [they] had shut down."
So we only know (C).
Hope that helps!
-t
P.S. We use the overall section question numbers. In other words, this should be posted as Q6, not Q2 (I changed it for you).