How much time should be spent carrying out Product Backlog refinement?

A. No more than 10% of the capacity of the Developers
B. Up to 10% of the capacity of the Developers in a typical Sprint, but as much as 90% in early Sprints
C. As much as the Product Owner and Developers agree is necessary to create enough ready Product Backlog items
D. As much as the Product Owner deems necessary to create enough ready Product Backlog items

Correct answer: C

This is not answered by Scrum. The Scrum guide prior to 2020 suggested 10% of the capacity of the Developers as normal but this was never a rule. The Scrum Team needs to find an appropriate level to ensure they have enough ready Product Backlog items for Sprint Planning.