You have been assigned as a new project manager for a multi-phase project that is midway through phase 3 of 5 phases. While the overall work of the team seems pretty good, you feel that phase 3 is starting to drift from the original plan. You set up a meeting with the project sponsor to discuss your concerns. The sponsor is surprised and agrees that phase 3 includes work that was not documented in the original agreement. To prove this, the sponsor refers you to which document?

A: Requirements traceability matrix B: Project management plan C: Statement of work D: Project scope statement