How much of the Sprint Backlog must be defined during the Sprint Planning event? (Choose the best answer)

How much of the Sprint Backlog must be defined during the Sprint Planning event? (Choose the best answer)
A . Enough so the Developers can create their forecast of what work they can do.
B . Just enough tasks for the Scrum Master to be confident in the Developers’ understanding of the Sprint.
C . The entire Sprint Backlog must be identified and estimated by the end of Sprint Planning.
D . Just enough to understand design and architectural implications.

Answer: A