According to the PMBOK® Guide, both stakeholder management and risk management are iterative processes that continue throughout the entire project lifecycle. Project environments are dynamic, and new information must be captured as soon as it is identified.

Why Choice B is correct:

Stakeholder Register: Since this is a " new " stakeholder, the Project Manager must first perform the Identify Stakeholders process. Adding them to the Stakeholder Register ensures their influence, interests, and communication requirements are documented and managed moving forward.

Risk Register: One of the primary responsibilities of a stakeholder is to provide expertise and perspective. If a risk is identified—regardless of when the stakeholder joined the project—it must be formally recorded in the Risk Register as part of the Identify Risks process. Once recorded, the risk can then be analyzed (qualitatively and quantitatively) to determine the appropriate response.

Analysis of other options:

A (Add to lessons learned at completion): This is a passive approach. Lessons learned are for future projects; the risk needs to be managed now to protect the current project’s success.

C (Complete proper testing): This jumps to a solution before the risk has been analyzed. Testing is a risk response (mitigation/appraisal), but the PM must first document and assess the risk before deciding that testing is the correct course of action.

D (Ignore the risk): This is a violation of professional responsibility. Stakeholders can emerge at any time (e.g., a new regulatory officer or a replacement department head), and their input is valid regardless of their presence at the project ' s start.

By following Choice B, the Project Manager ensures that project documentation reflects the current reality of the project environment, maintaining the integrity of the Project Management Plan and ensuring all potential threats are visible to the team and sponsors.