The correct answer is B - Create a spike story to analyze the impact of the threshold requirement on current stories.
A "spike" is a research activity used in Agile to investigate a technical or functional uncertainty. In this case, the performance threshold requires exploration to understand its impact on multiple backlog items. Creating a time-boxed spike allows the team to analyze without prematurely committing to changes.
PMI Agile Practice Guide describes spikes as:
"A spike is a user story for time-boxed research or exploration. Teams use spikes when they need more information to estimate or deliver a story." (PMI Agile Practice Guide, Section 5.2 - Types of Backlog Items) Mike Griffiths adds:
"When a new requirement introduces uncertainty, such as performance constraints, creating a spike helps the team determine scope, risk, and impact before incorporating it into backlog stories." (PMI-ACP Exam Prep, Chapter 5 - Adaptive Planning) Other options:
* A prematurely alters acceptance criteria before understanding the impact.
* C leans toward big upfront design (non-agile).
* D skips the exploration phase and directly breaks into tasks.