Many of the activities performed during the preliminary investigation are still being conducted in (1) , but in much greater depth than before. During this phase, the analyst must become fully aware of the (2) and must develop enough knowledge about the (3) and the existing systems to enable an effective solution to be proposed and implementeD. Besides the (4) for process and data of current system, the deliverable from this phase also includes the (5) for the proposed system.

2（）

A．main symptom

B．root problem

C．final blueprint

D．data specification

两个等量异种点电荷位于x轴上，相对原点对称分布，正确描述电势随位置x变化规律的是图 [ ]

A.

B.

C.

D.