i feel your pain on this one, but don't forget the AND in the first sentence binds each of the topics to the MOST that begins the sentence.

most cats have fur and always have four feet. Fat Cat was not like most cats, he only had 3 feet.

for the author to be more explicit in the way you are inferring, the statement would read: most cats have fur. all cats have four feet. Fat Cat is not a cat because he didn't have four feet.

to bring it home..."most nurseries do this and also do that". you get the 'most' for the 'this' part AND for the 'that' part. you are interpreting the author to have said "most nurseries do this, but ALL nurseries do that".

answer choice (A) talks about "the way", which can incorporate MANY facets. how many hours a day, how many months a year, how much discipline, how much screen time vs. reading books. it's very general. these two people would definitely disagree about "the way", "the best way", "the only way" to teach kids. but what, specifically, would they disagree about? are they upset about the fact that kids shouldn't have a 3 month break for the summer? maybe something else?

if you read the stimulus by itself, you're brain should be screaming "this person wants discipline, this one doesn't" and answer (B), in my mind, best encapsulated that whereas (A) was more broad.

i have also used GPT to get some guidance, and it's hard to disagree here that both (A) and (B) are decent choices. on this test, you have to throw away some of your outside knowledge and common sense (at times). many LSAT questions are more of a "game" than they are "real world arguments".

"probably" feels like a "most" or a 50% or more situation. the best you could say intelligently is that DM "might" be HP's friend.

you are right that "probably" does not commit the author to a yes/no with this argument, but the inferred meaning tends more towards being wrong than being correct. on this technicality, you can't say the argument is strictly "invalid", but you can guess that it's wrong.

had it said "therefore DM is HP's friend" that is absolutely wrong from a logical standpoint. same if you concluded "therefore DM is not HP's friend", that is logically incorrect, it can not be determined.

this is NOT correct, because of the "zero is also fewer than half" logical argument. saying "fewer than half" does not guarantee "some". this is an absurdity of the english language, but it IS technically possible to say "less than half" and you are referring to "none".

said another way....

the lower boundary of "fewer than half" is actually ZERO, though it would be absurd to use "fewer than half" when you mean "none"

if this was the argument, it would be written:

composition of seawater changes more during interglacial periods.

the fact that this one includes "than it" is really just pointing to itself, it makes no sense.

yeah, i don't care how you slice it, the interglacial statement is absolutely not a well formed sentence. if it had another lead-in or something, i totally get it.

however, don't get hung up on details. mistakes happpen.