What is "story splitting," and why is it useful in Agile planning?

A The practice of breaking down a large user story into smaller, independently deliverable pieces, making it easier to estimate, complete within a sprint, and deliver value incrementally B Story splitting means deleting half of a user story's description at random C It is a practice that requires combining all stories into a single giant story before any work begins D Story splitting can only be performed by the Scrum Master, never the team