Explanation
Correct answer: D.
Choice D is the best answer because it most logically completes the text’s discussion of the identification of maize’s wild ancestor. In this context, to "confirm" means to establish the truth or correctness of something. The text explains that maize "shows so little resemblance to any wild plant that genetic research was necessary" to establish its ancestry, which was ultimately traced to teosinte grass. This context conveys the idea that scientific verification was required to establish an ancestral relationship with certainty—that is, to confirm teosinte grass as maize’s ancestor.
Why the other choices are wrong
Choice A
Choice A is incorrect because to "acquire" means to obtain or gain possession of something. Although their research likely required scientists to acquire samples of maize and teosinte grass, the text does not suggest that this was the ultimate goal of their work, which instead probed the connection between the two plants.
Choice B
Choice B is incorrect because to "develop" means to create something or to promote the growth of something, and the ancestral relationship between teosinte grass and maize already existed as a biological fact in the deep past, which scientists then verified through research; because this relationship already existed, the scientists can’t be said to have either created it or encouraged its growth.
Choice C
Choice C is incorrect because to "attract" means to entice something or to bring about a relationship or connection between two things, while the ancestral relationship between teosinte grass and maize already existed as a biological fact; rather than bringing about the relationship between the two plants, the scientists instead verified the prior existence of it.