A cost-plus contract is a type of contract where the buyer agrees to reimburse the seller for the actual costs of the work plus a fee, which can be fixed, percentage, incentive, or award based. This type of contract has the highest risk for the buyer because the buyer has no control over the cost or quantity of the work and the seller has little incentive to control the costs or complete the work efficiently. The seller may inflate the costs or prolong the work to increase the fee. The buyer may end up paying much more than the estimated budget or the market value of the work. Reference = CompTIA Project+ PK0-005 Certification Study Guide, Chapter 9: Project Procurement Management; CompTIA Project+ Certification Exam Objectives, Domain 3: Project Execution, Objective 3.3: Execute procurement activities.

Agile is a methodology that emphasizes iterative and incremental development, customer collaboration, and responsiveness to change. Agile is suitable for developing a minimum viable product (MVP), which is a version of a product with just enough features to be usable by early customers who can then provide feedback for future product development. Agile allows the project sponsor to deliver an MVP quickly and test it with real users, and then adapt the product based on the feedback and changing requirements. Agile also reduces the risk of wasting time and resources on a product that does not meet the customer's needs or expectations123.
References = CompTIA Project+ Study Guide: Exam PK0-005, 3rd Edition, Chapter 2: Project Methodologies, p. 55; What is a Minimum Viable Product (MVP)? | Agile Alliance; Minimum Viable Product (MVP): What is it & Why it Matters - Atlassian

Explanation
Regression testing is a type of testing that is done on an existing system to ensure that the previous functionality still works after a change has been made. Regression testing is a process of retesting or verifying that a software system or application still performs as expected after it has been modified or updated with new features, bug fixes, patches, etc. Regression testing can help to detect any errors or defects that may have been introduced by the change and ensure that no functionality has been broken or degraded.

The waterfall methodology is a project management framework that follows a linear and sequential process,
where each stage of the project must be completed before moving on to the next one. The stages of the
waterfall model are initiation, planning, execution, and closure, as described in the question12.

The program manager should first obtain details from the owner of the project that is causing the delay, such
as the root cause, the impact, the mitigation plan, and the revised timeline. This will help the program manager
to assess the situation, communicate with the stakeholders, and adjust the program schedule accordingly.
Updating the critical path, applying contingency reserves, and reestimating epic user stories are possible
actions that the program manager may take after obtaining the details, depending on the severity and duration
of the delay. However, they are not the immediate next steps, as they require more information and analysis.
References = CompTIA Project+ Study Guide: Exam PK0-005, Third Edition, Chapter 10: Executing the
Project, page 2431; Dealing with delays - Project Management Institute2