Explanation
Correct answer: D.
Choice D is the best answer. “Demonstrating” means “showing,” and the text describes how de Santana disproved a previous belief in only one species of electric eel by showing that three electric eel species actually exist.
Why the other choices are wrong
Choice A
Choice A is incorrect. Pretending that there are three species of electric eel might be a fun game for marine biologists, but it wouldn’t prove the existence of more than one species.
Choice B
Choice B is incorrect. Complaining won’t prove anything about eels, so de Santana could not have proved wrong the idea of only one species of electric eel by complaining about it.
Choice C
Choice C is incorrect. “Requiring” means “needing.” It wouldn’t make sense to say that de Santana “needed” there to be three distinct species of electric eel.