一道CR

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. Therefore, 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?

A.      Doctors who are general practitioners rather than orthopedists are
        less likely than orthopedists to judge the stability of an ankle fracture correctly.

B.      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.

C.      X-rays of patients of many different orthopedists working in several
        hospitals were reviewed.

D.      The healing of ankle fractures that have been surgically repaired is
        always checked by means of a follow-up x-ray.

E.       Orthopedists routinely order follow-up x-rays for fractures of bone
        other than ankle bones.

不是很明白为什么是c，望指点

证明证据的有效性也是加强的一种

A，全科医生没有骨科医生判断准确性高，如果证据样本是来自全科医生的，就说明证据有效性是片面的，值得质疑的，是削弱

B，重复了一遍论据，跟别人讲道理翻来覆去说车轱辘话能加强么？

C，说明了证据样本来源广泛可靠，也就加强了论证

D，have been surgically repaired无关

E，fractures of bone
            other 无关