Planning to take it in June for the first time, and would be interested! Also in the Midwest :)

C says that the same amount of fat was consumed by both the people who ate less red meat and the people who didn’t eat less red meat.

D says that more fat was consumed by people who ate less red meat (so we assume no change in diet for the people who didn’t eat less red meat).

A isn't airtight because you're assuming that all vacuum tubes can have the preferable/comparable rule applied to them. The rule only applies to components with better heat resistance than semiconductors, so the rule only actually applies to SEVTs.

The last sentence gives you information about the set of vacuum tubes, but we need to apply that information to SEVTs in order to use that information with the preferable/comparable rule. It's a weird one, because we presume from an outside perspective that we'd want components without better heat resistance to still be comparable to be preferable, but the stimulus doesn't give us that.

A quick analogy that I hope gets the idea across better is this:

-Small dogs are fluffier than cats.

-Pets that are fluffier than cats are preferable as long as they are comparably nice.

-All dogs are not nicer than cats.

At this point, we can infer that small dogs are not preferable to cats, since they are fluffier and not nicer.

We do not have a rule for dogs that are not fluffier than cats, so there could be another rule that says "Pets that are not fluffier than cats are preferable as long as they are not comparably nice".

We just don't have any basis for evaluating not fluffy dogs, so a statement like "Dogs are not preferable to cats" might not be entirely accurate.

Most means greater than 50% regardless of how many options there are. So if most girls like pink, that means at least >50% of the girls like pink.

It may help you to view most as effectively the “majority.” 4 girls liking pink, 3 liking gold, and 3 liking yellow would mean that a plurality of girls like pink—not a majority (so not most).

For your other one, your argument is this:

Most men like black. Most women like black. Therefore, some women are men.

It would be visualized as this:

Men —m—> black

Women —m—>black

Women ←s→ Men

That’s an invalid argument, and it is not the format of formal argument #6.

The proper format results in you ending up with the same subject being the “most” twice.

A more accurate one would be:

Most men like black. Most men like women. Therefore, some men who like black also like women.

Men —m—> black

Men —m—> women

black ←s→ women