31. Which statement from the passage best supports the author's assertion that it took "humans and their ingenuity" to destroy billions of passenger pigeons? A. "Technology doomed these birds as the telegraph sent out word that the great migration had begun and the railroads brought hunters." B. "Preserved DNA would have to be genetically engineered to achieve the traits passenger pigeons once had." C. "Even if that technique worked, huge flocks of pigeons would have to be reproduced because that was the survival strategy for this animal." D. "It was an invasion of multitudes that unnerved humans cowering below."