The team decides a story is too big to do in one iteration. The correct technique to apply at this point is:

When a user story is too large to be completed within a single iteration, the correct agile technique is story decomposition. This process involves breaking down a large story (often called a compound story or an epic) into smaller, more manageable stories. Each resulting smaller story should still be independent, negotiable, valuable, estimable, small, and testable (INVEST). This allows the team to deliver value incrementally, improve estimation accuracy, and reduce the risk associated with large, complex work items.

A. MoSCoW approach: This is a prioritization technique (Must have, Should have, Could have, Won't have) used to rank features, not to break down a single large story.
C. Epic analysis: While an epic (a very large story) is analyzed, "epic analysis" is not a formal technique. The action of breaking it down is called decomposition.
D. Story partitioning: This is a specific strategy or method of decomposition, but "story decomposition" is the name of the overarching, fundamental technique itself.

1. IIBA®

Agile Extension to the BABOK® Guide

Version 2

2017.

Section 7.1

Story Decomposition (Page 107): "Story decomposition is a technique to represent the requirements for a solution at different levels of abstraction... Stories that are too large to be completed in a single iteration are decomposed into smaller stories until they are the right size for the team to complete in an iteration." This directly supports the correct answer.

Section 7.1.3

Elements (Page 108): The guide lists common ways to decompose stories

such as by user role

workflow steps

or business rule complexity

which reinforces that decomposition is the primary technique.

Section 5.3

Prioritization (Page 81): This section describes various prioritization schemes

including MoSCoW

confirming its purpose is for ranking relative importance

not for sizing or splitting work items.