According to the Scrum Guide, the time-boxed events in Scrum are Sprint Retrospective, Sprint Planning, and Daily Scrum. These events have a maximum duration that cannot be exceeded. The other options are not time-boxed events in Scrum, as they are either not part of Scrum (such as Release Planning, Release Retrospective, Sprint Testing, and Sprint 0) or not events at all (such as Definition of Done).

According to the Scrum Guide, every Scrum Team should have the competencies and skills needed to deliver an Increment in a Sprint. This means that the Developers can work on any aspect of the product without depending on others outside the team. The other options are not valid descriptions of what every Scrum Team should have, as they either imply that the Developers work in silos or rely on external people (such as a lead developer or representatives from different departments).

The correct answer is D. 10 or fewer. According to the Scrum Guide 20201, ''The Scrum Team is small enough to remain nimble and large enough to complete significant work within a Sprint, typically 10 or fewer people.'' The other options are outdated or incorrect. Option A was based on the previous version of the Scrum Guide, which suggested a range of 3 to 9 developers2. Option B is too vague and does not account for the upper limit of team size. Option C is too specific and does not allow for flexibility.

There are no activities that a Product Owner would typically undertake in the phase between the end of the current Sprint and the start of the next Sprint, because there is no such phase. The next Sprint starts immediately after the current Sprint, without any gaps or breaks. The other options are either activities that occur during a Sprint (such as refining the Product Backlog) or activities that are not consistent with Scrum (such as working with Quality Assurance departments or updating project plans).

The correct answer is A, because the best way the Scrum Master can ensure that the Development Team communicates effectively with the Product Owner is to monitor communications between them and facilitate direct collaboration. The Scrum Guide states that ''the Scrum Master serves the Product Owner in several ways, including ... facilitating Scrum events as requested or needed.'' Therefore, the Scrum Master should help the Development Team and the Product Owner interact regularly and productively during the Sprint Planning, Daily Scrum, Sprint Review, and Sprint Retrospective events.