Final answer:
In Continuous Delivery, Sprint Planning should occur every iteration to determine the work to be done within that period, whereas other events like System Demos or Program Increment Planning do not occur every iteration.
Step-by-step explanation:
The Continuous Delivery Pipeline event that should happen every iteration is D) Sprint Planning. Continuous Delivery is a part of the Agile methodology where updates to the software are continuously integrated, tested, and delivered to the customer.
Sprint Planning is crucial to this approach as it happens at the start of every sprint (iteration) to determine what work will be done during that time period. System Demos are typically done at the end of an iteration to showcase the work done, Inspect and Adapt is an event for problem-solving cycle and continuous improvement often conducted at the end of the Program Increment (PI), and Program Increment Planning is a larger event that kicks off a new PI cycle and is not held every iteration.