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

圆柱齿轮的齿和轴线平行，适用于相交轴之间的传动。