Renting equipment until the critical piece is repaired is a "Mitigate" response. Mitigation involves taking actions to reduce the impact or likelihood of a risk event. In this case, renting equipment is a way to reduce the impact of the equipment breakdown on the project's timeline and execution, thereby ensuring that the project can continue with minimal disruption.
PMI's guidelines describe mitigation as a strategy to reduce the severity or probability of a risk, making it a suitable response in this scenario.

Pure risks

Explanation
The project's contingency allowance is a provision in the project budget that is intended to cover known risks that may affect the project costs. The risk of increased fuel costs was identified and included in the contingency allowance, so the project manager should use it to process the freight invoices at the actual shipping costs. This is the best way to handle the risk without affecting the project scope, schedule, or quality.
Requesting a formal change order from the customer (option B) is not necessary, as the project budget already has a provision for this risk. Processing the freight invoices for the budgeted amount and hoping the shipping company will forgive the difference (option C) is unethical and unprofessional, as it violates the terms of the contract and the PMI Code of Ethics and Professional Conduct. Asking the project sponsor to cover the additional shipping costs on the company's reserves account (option D) is also not appropriate, as the company's reserves are meant for unknown risks that are beyond the project's control, not for known risks that are already accounted for in the project budget. References: PMI, The Standard for Risk Management in Portfolios, Programs, and Projects, 2019, p. 72; PMI, A Guide to the Project Management Body of Knowledge (PMBOK Guide), 6th ed., 2017, p. 252.
The project manager should use the contingency allowance to cover the additional shipping costs, as it was specifically included in the project budget for such risks. This approach avoids requesting unnecessary changes or relying on external sources to cover the cost overrun.

In this situation, the departure of a key project resource was an anticipated risk, and a transition plan was established as a response. However, implementing this plan has introduced new risks, known as secondary risks, which may impact the completion dates of other project-related tasks. According to PMI's risk management framework, it's essential to address these secondary risks in alignment with the predefined risk management plan. This involves assessing the new risks' probabilities and impacts, determining appropriate response strategies, and updating the risk register accordingly. By systematically managing secondary risks as outlined in the risk management plan, the project manager can mitigate potential adverse effects on the project's schedule and objectives.
PMI Risk Management Study Guide References:
The PMI-RMP Exam Preparation Study Guide highlights the necessity of managing secondary risks, stating that "secondary risks should be identified, analyzed, and planned for in the same manner as primary risks, ensuring that all potential threats to project objectives are adequately addressed."