Final answer:
In Agile methodologies, a Program Increment is analogous to a Sprint at the team level, with the former relating to the Agile Release Train and the latter to a single Agile team's efforts to deliver product increments.
Step-by-step explanation:
A Program Increment (PI) in the Agile framework corresponds to a specific period during which an Agile Release Train (ART) delivers incremental value in the form of working, tested software and systems. The PI is to the ART what an Iteration (or Sprint) is to a team-level process within Agile methodologies. In this context, the correct answer to 'A Program Increment relates to the Agile Release Train like an Iteration relates to what?' is B) Sprint.
A Sprint is a time-boxed period used by a team to implement and deliver a discrete product increment, typically lasting from one to four weeks. Just as the ART operates on PIs to align teams to a shared mission via a single Program Backlog, individual Agile teams use Sprints to manage and execute work from their Team Backlog. This works within the Scaled Agile Framework (SAFe), which helps larger organizations implement Agile at scale.