B is more of a weakening answer choice. It's giving an alternative point as to why they haven't received government funding. B is weakening the argument by saying that it's not because of the large corporation's influence but rather because of how "funding is always subject to change". C actually strengthens the argument a lot. If you look at the last few sentences where it states the premise "since large corporations have made it a point...". C is saying "The only research projects whose government funding has been severely curtailed are those that large corporations have made it a point to discourage" and that strengthens the argument because it's removing room for any other explanations.

Answer choice B says "manufacturers should be held responsible only for the preventable consequences of their actions". The word "only" is a necessary condition indicator so it follows a necessary condition and the words before it are the sufficient condition.

the music critic is challenging the conclusion that the professor made (rap music being individualistic and nontraditional) by saying there are things they didn't take into observation. the critic is not only challenging the point, they're also adding more points the professor failed to consider. so essentially how I understood it is, he's disagreeing with the professor's conclusion especially since he used "but" and he's adding extra info the professor missed. the critic is basically saying, "how can you come up with this conclusion when there are things you didn't acknowledge/missed that if acknowledged, would lead to a different conclusion".