Explanation
Prototyping is a tool or technique that could have been used by the business analyst to avoid the situation of unclear and conflicting requirements. Prototyping is the process of creating a simplified and partial version of the product or system that can be used to elicit, validate, and refine the requirements. Prototyping can help the business analyst and the stakeholders to visualize the solution, to identify and resolve any issues or gaps, and to reach a common understanding and agreement on the requirements. References: PMI Professional in Business Analysis (PMI-PBA)
Examination Content Outline1, page 18; Business Analysis for Practitioners:
A Practice Guide2, page 94.

Explanation
A change control process is a process that could help manage the situation of scope creep. Scope creep refers to the problem experienced on many projects when the size or complexity of the original product description grows. Scope creep can have negative impacts on the project schedule, budget, quality, and stakeholder satisfaction. A change control process is a process that defines how changes to the project scope, requirements, deliverables, or other configuration items are requested, evaluated, approved, implemented, and monitored. A change control process can help the business analyst and the project team to manage the expectations of the stakeholders, to assess the impact and feasibility of the changes, to prioritize and implement the changes, and to communicate the changes to the relevant parties. References: PMI Professional in Business Analysis (PMI-PBA)
Examination Content Outline1, page 23; Business Analysis for Practitioners: A Practice Guide2, page 131.

According to the PMI Professional in Business Analysis (PMI-PBA)Examination Content Outline, one of the tasks under the domain of Traceability and Monitoring is to "Track the status, priority, and disposition of requirements and issues, and communicate updates as necessary" (Task 1). This implies that the business analyst is responsible for ensuring that the requirements are delivered as stated and that any changes or issues are communicated to the relevant stakeholders. One of the techniques that can be used to perform this task is the traceability matrix, which is a table that shows the relationships between requirements and other project artifacts, such as design documents, test cases, or deliverables. A traceability matrix can help the business analyst to verify that all the requirements are covered by the test cases and that the test output matches the expected results. Therefore, the technique that the business analyst could have used to ensure that requirements were delivered as stated is the traceability matrix.