Regarding B… Yeah, I’ve tried and tried to find an intuitive explanation for this, and I’ve never yet found one. Basically the answer boils down to “Because the math says so” and every attempt to explain that in practical terms always comes down to drawing a light cone diagram and showing the causality paradox in geometric terms. I find this intensely dissatisfying because it’s really just visualizing the math without actually framing it in any way that’s truly comprehensible beyond “Trust me bro.”

This video, while a little over padded with fluff, does contain the best and most comprehensible version of this explanation that I’ve seen, but I’d love for someone to be able to put it in terms that actually make sense without just drawing lines on a graph and gesturing at them. Maybe that just isn’t possible. Perhaps the whole point is that FTL breaks the laws of the universe and our understanding of reality is necessarily constrained by those same laws.

Edit: OK, this video is a much better version of the explanation I described. I still find that explanation unsatisfying, but it is at least highly comprehensible.