The correct answer is A - Explore options for increasing knowledge in the next iteration's backlog.
One of the key principles of Agile is continuous learning and improvement. When the team identifies a skills gap during a retrospective, the appropriate response is to turn that learning need into actionable items in the upcoming backlog. This can include training, pairing, spikes, or experimenting in a time-boxed way during the next iteration.
From the PMI Agile Practice Guide:
"Teams should regularly inspect their tools, practices, and outcomes and incorporate improvement actions into their backlog. Continuous learning is a shared responsibility." (PMI Agile Practice Guide, Section 3.5 - Retrospectives & Section 6.2 - Coaching the Agile Team) Mike Griffiths also supports this:
"Improvement actions should be planned, prioritized, and implemented like any other work. Skills development should be addressed through backlog items such as training, spikes, or pairing." (Mike Griffiths, PMI-ACP Exam Prep Book, Chapter 7 - Continuous Improvement) Why the other options fall short:
* B adds scope mid-sprint, which violates Agile principles (sprint backlog should remain stable).
* C may be viable long-term, but doesn't address the team's agreed goal of learning the tool.
* D brings in an external expert rather than empowering the team to grow their capabilities.