_______ Lily _______ Lucy is going with you because one of them must stay at home. [ ]

A. Not only; but also

B. Neither; nor

C. Both; and

D. Either; or

概率法主要是把事故后果的分析与实际运行中的事故发生概率分析结合起来，根据系统各组成要素的（），确定系统发生事故的概率。