When it comes to SAT question types, tone and attitude questions are routinely among the most predictable in terms of which answers are likely to be both correct and incorrect. When you take them apart, the vast majority of tone questions boil down to “positive vs. negative,” and then to what degree.
Furthermore, incorrect answer choices are highly patterned. Certain words almost invariably signal wrong answers. Many of these fall into the infamous “extreme” category (e.g. “furious” and “awed”), but others are at odds with the framework of the test in other ways. And answer choices that indicate a lack of interest on the author’s part fall squarely into this category.
Think of it this way: pretty much on principle, professional authors choose to write about their subjects because they care about them. By definition, they are engaged with what they are writing about. Otherwise, they wouldn’t write about it! So while an author may have a clearly negative attitude toward a subject, or write in a neutral (analytical, detached) tone, almost never will they simply not care. As a result, answers such as “apathetic” and “indifferent,” which suggest a complete lack of interest, are almost always incorrect.
This also goes for P1/P2 relationship questions. Paired passages are selected for the test specifically because they have some sort of relationship — most often a conflicting relationship — to one another. If the authors were indifferent to one another’s subject matter, the passages never would have shown up on the test in the first place.
The primary exception to this rule comes in fiction passages. Fictional characters, unlike authors, can very well demonstrate a lack of interest in something during the course of a passage. If the text clearly indicates that is the case, you can and should pick an answer reflecting that fact.