Thanks for the question! It’s not exactly that (B) reverses sufficient and necessary as is used in the passage. The conditional relationship in the passage is that if research results aren’t shared, then humans might suffer unnecessarily, which would be
Research kept confidential —> Human suffering
And the reverse of that is
Human suffering —> Research kept confidential
Which isn’t exactly what (B) is saying. (B) is wrong because it talks about “the most important moral principle” being to prevent human suffering, but we aren’t told anything about what the most important moral principle is. And so that sufficient condition can’t ever get triggered based on what we know in the stimulus. It’s just an irrelevant condition that can’t apply here. And that’s what makes (B) wrong.
Hope this helps! Feel free to ask any other questions that you might have.