The (1) is a general description of the

问题：

The (1) 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 (2) . In a workflow system, a process is specified using the process definition tool. Usually, processes are defined in terms of a (3) , which consists of (4) indicated using a circle, and (5) shown as a rectangle. These two components can be linked by means of a directed arc.

2（）

A．tasks

B．processes

C．workflow threads

D．workflow engines