I believe I've identified another reason for eliminating answer B that is--to me at least--much more obvious than the reasoning the explanation offered: the stimulus specifies "such criticism" as that of "a politician criticizing his or her political opponents." Answer B uses as its subject the very general "sincere critics," meaning these critics could be politicians or they could be members of the general public, or pundits. The stimulus only tells us that such criticisms coming from politicians and directed at their opponents are insincere, meaning that there could in fact be sincere criticism of politicians on these grounds coming from another group (e.g. general public, pundits, etc.). Does my logic here hold water?

For question number 4, would it also be correct to end up with M-->/F. As far as I can tell that is logically equivalent to /M-->F. I know that technically speaking "not fat" is a different superset from "fat," so this answer would involve changing the necessary as opposed to the sufficient condition. That being said, I cannot find a logical flaw in answering /M-->F, which also has the added benefit of translating more clearly to english. Please let me know if you see any issues here!

Am I crazy or is there a typo in question 2:

It currently reads "The composition of seawater changes more slowly than it does in interglacial periods."

I'm fairly adept when it comes to grammar and it seems to me that the "than it does" is not only extraneous but also grammatically, or at least syntactically, incorrect. I understand that the point of the question is that the comparison between glacial and interglacial periods is implied, not explicit, but it seems to me that someone left in the "than it does" from the explicit version when drafting the implied version. Shouldn't the sentence read "The composition of seawater changes more slowly in interglacial periods."? The "than it does" makes the sentence incomprehensible.

If I'm making a mistake, I'd greatly appreciate it if someone could explain to me what I'm missing.