During a Sprint, when is new work or further decomposition of work added to the Sprint Backlog? A: As soon as possible after they are identified. B: During the Daily Scrum after the Development Team approves them. C: When the Product Owner identifies a new work.
It can't be C, because the Product Owner is not in a position to add work to the Sprint Backlog. Only the Development Team can do that, because they wholly own that backlog. Once a PO identifies new work, he or she can add it to the Product Backlog and request that the Development Team estimate it. It can then be brought into a future Sprint Planning session.
B is a plausible answer. The Daily Scrum is an inspect/adapt opportunity and it can certainly lead to the team revising their Sprint Backlog. However, it is not the *only* opportunity for them to do so. The Development Team can and should update their Sprint Backlog on an ongoing basis.
Therefore the best answer is probably A, although for better clarity I think it should really say "As soon as possible after they are identified by the Development Team".