Often patients with ankle fractures that are stable, and thus do not require surgery, are given follow-up x-rays because their orthopedists are concerned about possibly having misjudged the stability of the fracture. When a number of follow-up x-rays were reviewed, however, all the fractures that had initially been judged stable were found to have healed correctly. Ttherefore, it is a waste of money to order follow-up x-rays of ankle fracture initially judged stable. Which of the following, if true, most strengthens the argument? ['The healing of ankle fractures that have been surgically repaired is always checked by means of a follow-up x-ray.', 'Doctors who are general practitioners rather than orthopedists are less likely than orthopedists to judge the stability of an ankle fracture correctly.', 'X-rays of patients of many different orthopedists working in several hospitals were reviewed.', 'Many ankle injuries for which an initial x-ray is ordered are revealed by the x-ray not to involve any fracture of the ankle.']