Explanation: The disaster recovery (DR) process should always include plan maintenance. Plan maintenance is the process of updating, reviewing, testing, and improving the DR plan to ensure its effectiveness and efficiency. Plan maintenance is essential for the DR process, as it helps to keep the DR plan aligned with the current business needs, objectives, and environment, as well as the best practices and standards. Plan maintenance also helps to identify and resolve any gaps, issues, or weaknesses in the DR plan, as well as to incorporate any feedback, lessons learned, or changes from the previous DR tests or events. Plan maintenance should be performed regularly, as well as after any significant changes in the organization, such as new systems, applications, processes, or personnel. Periodic vendor review, financial data analysis, and periodic inventory review are not activities that should always be included in the DR process. Periodic vendor review is the process of evaluating the performance, quality, and reliability of the vendors that provide services or products to the organization, such as backup, recovery, or cloud services. Periodic vendor review is important for the DR process, as it helps to ensure that the vendors meet the contractual obligations and service level agreements (SLAs) of the organization, as well as to identify and mitigate any risks or issues associated with the vendors. However, periodic vendor review is not a mandatory activity for the DR process, as it depends on the organization’s reliance on external vendors for its DR strategy. Financial data analysis is the process of examining, interpreting, and reporting the financial data of the organization, such as revenue, expenses, assets, liabilities, or cash flow. Financial data analysis is important for the DR process, as it helps to determine the budget, resources, and priorities for the DR plan, as well as to measure the financial impact and return on investment (ROI) of the DR plan. However, financial data analysis is not a mandatory activity for the DR process, as it depends on the organization’s financial goals and constraints for its DR strategy. Periodic inventory review is the process of verifying, updating, and documenting the inventory of the organization, such as hardware, software, data, or supplies. Periodic inventory review is important for the DR process, as it helps to ensure that the organization has the adequate and accurate inventory for its DR plan, as well as to identify and address any inventory shortages, surpluses, or discrepancies. However, periodic inventory review is not a mandatory activity for the DR process, as it depends on the organization’s inventory management and control for its DR strategy. References: Official (ISC)2 CISSP CBK Reference, Fifth Edition, Domain 7, Security Operations, page 734. CISSP All-in-One Exam Guide, Eighth Edition, Chapter 7, Security Operations, page 696.