The correct answer is A. A control plan . The CSSBB source states that the project control phase is necessary in order to sustain the project gains and that the control plan must remain a living document to monitor and control the process. It also says that a responsible person should be placed in charge of the control plan, and that the process owner is often the best person for that role. In the closing-phase guidance, the source specifically includes identifying the process owner , creating updated work instructions and procedures , training affected personnel , and attaining agreement between the team members and process owner .

These points directly support the idea of keeping the improved process in place and transferring ownership to those who will use and maintain it. A control chart is only one monitoring tool, not the full sustainment document. A process change order is an administrative record, and FMEA is a risk-analysis tool. Therefore, the document intended to sustain the gains, discourage tampering, and hand off responsibility is the control plan . The verified answer is A .