Which three elements can a job chain process involve?

Which three elements can a job chain process involve? (Choose three)

A.
an event

B.
a schedule

C.
a program

D.
another chain

E.
a lightweight job

Explanation:
Don’t really understand the answer so far.
Defining Chain Steps
After creating a chain object, you define one or more chain steps. Each step can point to one
of the following:
A Scheduler program object (program)
Another chain (a nested chain)
An event schedule, inline event, or file watcher