Explanation
Correct answer: A.
Choice A is the best answer because it most logically completes the text’s discussion of the fossil site from which the evidence about brood care in K. popovi was recovered. In this context, “fruitful” means abundantly productive. The text indicates that the researchers drew their evidence from fossils found in China’s Haifanggou Formation, a location that has yielded a vast diversity of fossils. The information about the site yielding a vast diversity of fossils supports the characterization of the Haifanggou Formation as particularly productive, or fruitful.
Why the other choices are wrong
Choice B
Choice B is incorrect because there is nothing in the text to support characterizing the Haifanggou Formation as a site that is particularly “unassailable,” or not open to attack, question, or criticism. The text emphasizes that the site has yielded a vast diversity of fossils, suggesting that it is a particularly productive location for fossil hunters, not that it cannot be challenged.
Choice C
Choice C is incorrect because there is nothing in the text to support characterizing the Haifanggou Formation as a site that is particularly “obscure,” or poorly understood or relatively unknown. In fact, the text notes that the Haifanggou Formation has yielded a vast diversity of fossils, suggesting that the site is not an obscure one.
Choice D
Choice D is incorrect because “quantified” means expressed or measured as a quantity, which does not describe the productiveness the context calls for. Although the text indicates that the Haifanggou Formation has yielded a vast diversity of fossils, that fact suggests that the site can be characterized as particularly productive, not as particularly quantified.