The correct answer is A, because a Sprint Retrospective should be held at the end of each Sprint. The Scrum Guide states that "the Sprint Retrospective is an opportunity for the Scrum Team to inspect itself and create a plan for improvements to be enacted during the next Sprint. ... The Sprint Retrospective occurs after the Sprint Review and prior to the next Sprint Planning."

The correct answer is C, because if burndown charts are used to visualize progress, they track work remaining across time. A burndown chart is a graphical representation of the amount of work left to do versus the time available. It helps the Scrum Team monitor and forecast the progress toward the Sprint Goal.

According to the Scrum Guide1, an Increment is a concrete stepping stone toward the Product Goal. Each Increment is additive to all prior Increments and thoroughly verified, ensuring that all Increments work together. In order to provide value, an Increment must be usable. Multiple Increments may be created within a Sprint. The sum of the Increments is presented at the Sprint Review thus supporting empiricism. However, an Increment may be delivered to stakeholders prior to the end of the Sprint. The Sprint Review should never be considered a gate to releasing value. Therefore, the best description of an increment of working software is additional features in a usable state that complement those delivered in previous iterations.

The correct answer is A, because the Product Owner does not need to be present at the Daily Scrum. The Scrum Guide states that "the Daily Scrum is a 15-minute time-boxed event for the Development Team to synchronize activities and create a plan for the next 24 hours. ... The structure of the meeting is set by the Development Team and can be conducted in different ways if it focuses on progress toward the Sprint Goal." Therefore, the Daily Scrum is an internal event for the Development Team, and the Product Owner can attend only if invited by the Development Team.

A Developer is accountable for creating a plan for the Sprint, the Sprint Backlog, and organizing the work required to meet the Sprint Goal, as stated in the Scrum Guide: "Developers are the people in the Scrum Team that are committed to creating any aspect of a usable Increment each Sprint. The specific skills needed by the Developers are often broad and will vary with the domain of work. However, the Developers are always accountable for:
Creating a plan for the Sprint, the Sprint Backlog;
Instilling quality by adhering to a Definition of Done;
Adapting their plan each day toward the Sprint Goal; and,
Holding each other accountable as professionals."