The correct answer is D, because if a new Development Team decides that a Sprint Retrospective is unnecessary, the Scrum Master should begin facilitating productive and useful Sprint Retrospectives. The Scrum Guide states that "the purpose of the Sprint Retrospective is to plan ways to increase quality and effectiveness. ... During each Sprint Retrospective, the Scrum Team plans ways to improve product quality by adapting the definition of 'Done' as appropriate." Therefore, the Scrum Master should help the Development Team understand the value and importance of the Sprint Retrospective, and make it an engaging and constructive event.