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.
Reference:
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