This is descriptively inaccurate. The author says that Sibley’s work isn’t widely accepted, not that Sibley’s work brought the debate closer to resolution.

We know that one critic thinks that interpreting differences between populations is arbitrary, but we don’t know that most agree with this claim. Also, (B) only talks about P3, so it can’t be the main idea of the passage as a whole.

This is the main point of the passage. P1-P3 outline the debate between the lumpers and the splitters over the controversial issue of species classification, and P4 describes the practical implications of the debate.

The main point of this passage is not that Sibley has questioned a traditional view. Instead, the main point is the general debate between the lumpers and the splitters. Sibley’s view serves as an example of the splitter perspective that shows how the different perspectives yield different outcomes for species classification. The passage opens and closes with the general debate about species classification, which can help clue us in to the overall main point.

The main point of this passage is not that Sibley’s methods are revolutionary. Instead, the main point is the general debate between the lumpers and the splitters. Sibley’s view is just an example of one of the two general perspectives; his method is not the main point of the passage.