Explanation
The resource management plan is a component of the project management plan that describes how the project resources are acquired, allocated, monitored, and controlled. It also defines the roles and responsibilities of the project team members and the reporting structure. The resource management plan is an important input for managing project resources and resolving resource conflicts. If the project manager faces a situation where some key resources are not available for the project, he or she should consult the resource management plan and escalate the issue to the sponsor or other appropriate stakeholders. The sponsor can help the project manager negotiate with the functional managers or other resource providers to secure the required resources for the project. The sponsor can also authorize changes to the project scope,schedule, or budget to accommodate the resource constraints. The other options are not appropriate because they do not address the root cause of the problem and may lead to further delays or risks for the project. References: PMBOK Guide,
7th edition, section 9.1.3.1, page 309; PMI, PMP Exam Content Outline, 2021, Domain II: Process, Task 5.