Which of the following, if true, would cast the most doubt on the second theory? A. The Pteranodon was primarily a scavenger and so needed to forage for food on the ground. B. Flying while hunting for food would be highly inefficient use of energy expenditure for the Pteranodon. C. A Pteranodon was unable to walk for more than fifteen minutes without either resting or resuming flight. D. Walking would have left the Pteranodon vulnerable to predators. E. A closely related species of the Pteranodon had a wingspan greater than 25 feet, which precluded the formation of retractable wrists.