关于电力线，正确的说法是（）。

A.电力线并不是实际存在的的线，只是人们用来描绘电场的一种方法

B.电力从正电荷出发，经负电荷，再回到正电荷

C.电力线互相排斥，互不相交电力密集之处，表示场强大

D.电力线就是正电荷受电场力时的运动轨迹

The relational database model requires the data be (110) through programs that don’t rely on the position of the data in the database. This is in direct (111) to the other database mode, where the program has to follow a series of pointers to the data it seeks. A program (112) a relational database simply asks for the data it seeks; the DBMS performs the necessary searches and (113) the information. The (114) on how the search is done are specific to the DBMS and vary from product to product.

（111）是（）

A.conduct

B.contract

C.contrast

D.construct