The Product Owner is responsible for managing and refining the Product Backlog, which is the single source of truth for the plan of the product development. The Product Backlog is a living artifact that changes as the product and the market evolve. The Product Owner updates the Product Backlog continuously based on feedback, learning, and stakeholder needs. There is no separate project plan document in Scrum.

[Scrum Guide], section 3.1: ''The Product Backlog is an emergent, ordered list of what is needed to improve the product.''

[Professional Scrum Product Owner], chapter 5: ''The Product Backlog represents everything necessary to develop and launch a successful product.''

[What is a Product Backlog?]: ''The Product Backlog is a list of all things that need to be done within the project.''

The Scrum Guide states that ''Sprints are the heart of Scrum where ideas are turned into value''. It also states that ''Sprints have consistent durations throughout a development effort. A new Sprint starts immediately after the conclusion of the previous Sprint''. Furthermore, it states that ''Sprints are limited to one calendar month. When a Sprint's horizon is too long the definition of what is being built may change, complexity may rise, and risk may increase''. Therefore, the correct answer is B. The other options are not acceptable, as they contradict the Scrum principles of empiricism, self-organization, and adaptation.

The Scrum Guide, section 3.1. Sprints

Professional Scrum Product Owner I (PSPO I) Learning Path, section 2.2. The Product Owner and the Sprint

The Sprint Backlog is created during Sprint Planning, where the Developers select the Product Backlog items that they can deliver in the Sprint and create a plan for how to do the work.The Scrum Guide states that 'The Sprint Backlog is composed of the Sprint Goal (why), the set of Product Backlog items selected for the Sprint (what), as well as an actionable plan for delivering the Increment (how).'1The Sprint Backlog is owned and managed by the Developers, who can update it throughout the Sprint as more is learned.

1: The Scrum Guide2, page 15

2:The Scrum Guide

To say that an event has a timebox means that the event has a fixed duration that cannot be exceeded. The Scrum Guide states that 'All events are time-boxed events, such that every event has a maximum duration. Once a Sprint begins, its duration is fixed and cannot be shortened or lengthened.The remaining events may end whenever the purpose of the event is achieved, ensuring an appropriate amount of time is spent without allowing waste in the process.'1This means that the timebox sets an upper limit for the event, but the event can end sooner if the goal is met.

1: The Scrum Guide2, page 10

2:The Scrum Guide

According to Scrum.org, the Developers who will be doing the work are responsible for the sizing of Product Backlog items1. The Product Owner may influence the Developers by helping them understand and select trade-offs1. This implies that the Developers size the items after clarifying requirements with the Product Owner1.