The（）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（）. In a workflow system, a process is specified using the process definition tool. Usually, processes are defined in terms of a（）, which consists of（）indicated using a circle, and（）shown as a rectangle. These two components can be linked by means of a directed arc.

The workflow enactment service is the heart of a workflow system which consists of several（）

A．workflow engines

B．processes

C．workflow threads

D．tasks