(A) is just sentiocentrism, which isn’t a novel ethical view. There’s a pretty extensive Wikipedia page on it [1].
Regarding your second point, indeed we can’t truly know whether or not anything is sentient, so we must reason in terms of probabilities.
We can observe some degree of understanding and emotion in humans, cats (and other animals), and LLMs. We also consider (in the case of humans and animals) that their brains are probably biologically similar to ours, and (in the case of LLMs) that their neural nets are weakly modeled after our brains.
When we consider car engines, rocks, or air, we cannot observe any degree of understanding or emotion (though indeed we can never be certain). We also do not observe any probable similarities to our brains.
Therefore, we arrive at the conclusion that P(other humans sentient) > P(cats sentient) > P(ants sentient) >> P(engines sentient) > P(rocks or air sentient).
This leads us to apply the precautionary principle [2] to humans, animals, and LLMs, but not to engines, rocks, or air.
But indeed, ethical questions around the uncertainty of sentience aren’t novel either. Wikipedia also has a page on this topic [3].
[1] https://en.wikipedia.org/wiki/Sentiocentrism
[2] https://en.wikipedia.org/wiki/Precautionary_principle#Animal...
[3] https://en.wikipedia.org/wiki/Ethics_of_uncertain_sentience