求解新东方蓝皮55页上的一道语法题 麻烦牛牛解释下

8. Studies of the human “sleep-wake cycle” have practical relevance for matters ranging from duty assignments in nuclear submarines and air-traffic control towers to the staff of shifts in 24-hour factories.
(A) to the staff of
(B) to those who staff
(C) to the staffing of
(D) and staffing
(E) and the staff of

答案为什么是c ， a 为什么不对， range from....,to.......  这个结构中的assignments 和 staff 刚好平行啊

牛牛们 来讲下啊  谢谢

这里的staff作动词用，意思为给……调配干部，雇佣职员这样的意思，而staff作名词的意思为员工。然后the staffing 就是动名词，这样从意思上与形式上都与前文平行啦