Predictable flow in agile is achieved by reducing variability in story size and complexity. According to the PMI Agile Practice Guide (Section 5.7: Flow-based Agile and Kanban), working with small, similarly sized user stories increases throughput predictability and improves cycle time.

Mike Griffiths in the PMI-ACP Exam Prep Book (Chapter 6: Value-Driven Delivery) supports breaking large stories into smaller, testable chunks as a way to stabilize delivery and forecasting.

Option A is correct: small user stories reduce variability and support predictable flow.

Option B supports testability but doesn’t directly improve flow.

Option C and D are too broad or conceptual to specifically improve predictability.