Why is the answer A?

@Steph, Happy to help. The question asks us to identify the answer choice that describes what the author is primarily concerned with doing in the passage. From reading the text, we know that the author discusses three different theories that could explain the extinction of dinosaurs, but she also spends much more time on the third theory and goes into detail about why it's better than the other two. That's the basic gist of this passage. In looking at the answer choices, we want to find the answer that best matches our prediction for what the answer will be. Answer A says the author is describing three theories and explaining why the latest of these appears to be the best of the three. This is great; it's an excellent paraphrase of what we outlined as the primary purpose of the passage. This is our answer. Answer B is incorrect because it doesn't mention anything about the third theory and how the author likes it the most. This is a bad answer. Answer C is incorrect because the author does not outline the inadequacies of the third theory; rather, she provides lots of support for why it has greater explanatory powers than the other two do. This is a wrong answer. Answer D is incorrect because 1) it doesn't paraphrase what we predicted was the primary concern of the author and 2) the author doesn't even include a general assertion that theories must often be revised in light of new evidence. This answer is out. Answer E is incorrect because it fails to mention all three theories that are discussed in the passage. The author's primary concern is laying out the three theories and showing why the third is the best. This answer is out. Does this make sense? Let us know if you have any more questions!

Yes thank you!

@Steph, you're welcome!