The (29) is a general description of the a
题型：单项选择题
问题：
The (29) 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 (30) 。
30（）
A. workflow engines
B. processes
C. workflow threads
D. tasks