According to the Scrum Guide1, there are three roles in a Scrum Team:
The Product Owner
The Developers
The Scrum Master
The Product Owner is accountable for maximizing value resulting from work by Developers. Developers are accountable for creating a plan for the Sprint, the Sprint Backlog. The Scrum Master is accountable for establishing Scrum as defined in the Scrum Guide. They do this by helping everyone understand Scrum theory and practice, both within the Scrum Team and the organization. Every Scrum team must have a Product Owner and Scrum Master, as outcomes are affected by their participation and availability. The other options are false, as they imply that the Product Owner and Scrum Master roles are optional or interchangeable.

The correct answer is D, because the Scrum Guide states that "a Sprint is a container for all other events. Each event in Scrum is a formal opportunity to inspect and adapt something. These events are specifically designed to enable critical transparency and inspection. Failure to include any of these events results in reduced transparency and is a lost opportunity to inspect and adapt." Therefore, a Sprint is over when its time-box expires, regardless of whether all Product Backlog items or tasks are completed or not.

According to the Scrum Guide, a self-organizing Development Team chooses how to best accomplish its work, rather than being directed by others outside the team. The other options are not choices that a self-organizing Development Team makes, as they are either determined by the Scrum framework (such as Sprint length and Product Backlog ordering) or by collaboration with other roles (such as stakeholders for the Sprint Review and when to release).

According to the Scrum Guide, the action that the Scrum Master should take when the Team decides that a Sprint Retrospective is unnecessary is to begin facilitating productive and useful Sprint Retrospectives. The Sprint Retrospective is an essential event for the Scrum Team to inspect itself and create a plan for improvements to be enacted during the next Sprint. The Scrum Master is responsible for ensuring that this event takes place and that positive outcomes are achieved. The other options are not valid actions, as they either imply that the Scrum Master complies with or ignores the decision of the Team (such as complying with it, calling a meeting with senior management, or consulting with the Product Owner), which is not consistent with Scrum values and principles.

The correct answer is A, because the Scrum Guide states that "the definition of 'Done' is a formal description of the state of the Increment when it meets the quality measures required for the product." Therefore, non-functional requirements should be part of the definition of 'Done' and ensure every Increment meets them.