A. They consist of one or more Scheduler programs.
B. They are used to implement dependency scheduling.
C. They are used to implement time-based scheduling.
D. They are used to implement event-based scheduling.
E. None of the above.
答案：（B）
解析：
《Administrator’s Guide》 29.6 Creating and Managing Job Chains
Job chains是一个命名的一系列的任务,这些任务为了一个组合的目标而链接在一起.
chains是手段,通过它可以实现dependency based scheduling,即job的开始是依赖于之前的一个或多个job的输出.