If you apply lawgic everything after "Only if" is the necessary condition(conclusion). According to lawgic C sets our desired necessary(uniform national speedlimit set) as the sufficient.

The rule needs to fit in our established P>C

Answer C had it written as C>P

D explicitly states an analogous benefit. Meaning the analogy is still valid under D.

While E opens the door for not only a decreased benefit but also a possibility for price increases and things to go wrong.

Your confusion comes from the "Most weakens". The argument does not need to be destroyed, it just needs to be hurt. E doesn't ruin the argument, but it opens the door for it to become completely invalid. Doing way more than D does or ever could.

If you think all of these answers weaken the argument then you're making mistakes and you should review.

Also the difference between "weakens" and "most-weakens" is discussed in the foundations part of the course. He doesn't mention it now because it would be redundant.

The mass was changed, just barely. A lack of consensus on procedure does not stop the possibility of researchers coming up with similar estimates through different procedures.

You forgot that "birds cannot sing" translates to "/BS" before you apply the translation rule.

Birds cannot sing unless pastries cook themselves (/BS) (PC)

In lawgic after group 3 translation rule: BS->PC

You're just translating wrong

Question two is just a lot of basic concepts shoved together. He breaks down each one of them and there really isn't any room for confusion if you listen. Try watching it again if you're still confused.

I use "necessity" as a word synonymous with "superset" or the "right side in lawgic"

So when the scenario is, "Only High flying birds nest in the summit of the Andes" this scenario is saying that HFB's can nest anywhere they want, but only THEY can nest in the Andes.

When the scenario is, "The only high flying birds are the ones nesting in the Andes". Nesting in the Andes has now become a NECESSITY for even BEING an HFB.

Scenario one makes being an HFB the necessity, scenario two makes Nesting in the Andes a necessity.

I really don't understand the emphasis placed on indicator words. It seems to me that you only truly understand these things when you understand what the indicator words are doing to the grammar of scenarios that make them group 1 or 2.

You might be thinking,"well you changed a lot more than just only or the only". You're on the right track but the entire sentence changes because the words aren't interchangeable, they have two different meanings that REQUIRE changing the entire sentence. When compared in a vacuum they are almost the same, but with the context of a complete sentence they are very different.

One way of looking at it is treating "the rights" as a referential for the very specific right given to those of future generations.