Explanation
The business analyst should work with business stakeholders to collaborate in writing, reviewing, and executing UAT scenarios, providing feedback, and approval for release. This is because UAT scenarios are based on real-world use cases and expectations of how users will interact with and benefit from the solution.
Business stakeholders are best suited to provide input and validation for UAT scenarios, as they represent the end-users or customers of the solution. The business analyst should facilitate the collaboration process by defining the scope, format, and criteria for UAT scenarios, and ensuring that they align with the user stories and acceptance criteria. The business analyst should also collect and document the feedback and approval from business stakeholders, and communicate them to the development team. References:
https://trailhead.salesforce.com/content/learn/modules/user-story-creation/user-acceptance-testing

Support agents are critical for the BA to include in UAT because they are the end users of the Service Cloud enhancements and can validate whether the solution meets their needs and expectations. System developers and quality assurance testers are important for the development and testing phases, but they are not essential for UAT, which is focused on the business requirements and user feedback. References: Learn About User Acceptance Testing Unit, [User Acceptance Testing Strategies for Large Data Volume Scenarios], [Role of the BA in User Acceptance Testing]

Explanation
A functional requirement specification is a statement that describes what a product or service must do or provide to meet user needs or business objectives. It should be clear, concise, testable, and measurable. The option B is an example of a functional requirement specification because it describes what the portal should do (allow for partners to upload monthly sales reports) without specifying how it should do it or why it should do it. References:
https://trailhead.salesforce.com/content/learn/modules/salesforce-business-analyst-certification-prep/requirement

This answer states that following these steps is the process that the BA should follow to draft and finalize the requirements for implementing a new Service Cloud feature for Cloud Kicks. Reviewing information from the discovery means that the BA revisits the information or data that was collected during the discovery phase, such as business goals, stakeholder needs, pain points, opportunities, etc. Asking clarifying questions means that the BA seeks to understand and verify the information or data that was collected, and to resolve any ambiguities or conflicts among them. Drafting requirements means that the BA writes down the statements that describe what the solution must do or have to meet the business goals and stakeholder needs. Refining and confirming requirements means that the BA revises and validates the requirements with the stakeholders, and ensures that they are clear, concise, consistent, and complete. Prioritizing which requirements will be included in the minimum viable product means that the BA determines which requirements are essential or desirable for delivering a solution that provides value to the stakeholders, and which requirements can be deferred or excluded from the scope. References: https://trailhead.salesforce.com/en/content/learn/modules
/salesforce-business-analyst-quick-look/use-user-stories-to-capture-requirements