在一个等边三角形ABC顶点B、C处各放一个点电荷时，测得A处的电场强度大小为E，方向与BC边平行沿B指向C如图所示，拿走C处的电荷后，A处电场强度的情况是

A．大小仍为E，方向由A指向B

B．大小变为，方向不变

C．大小仍为E，方向由B指向A

D．无法确定

The （71） is a general description of the architecture of a workflow management system used by the WFMC, in which the main components and the associated interfaces are summarized. The workflow enactment service is the heart of a workflow system which consists of several （72）.

A．waterfall model

B．workflow reference model

C．evolutionary model

D． spiral model