Final answer:
The base branch for a feature branch is found in the Project linked to the User Story, which allows overriding the default master branch. Dave can select UAT as the base during the creation of the new branch if the repository hosting service or project management tool supports it.
Step-by-step explanation:
Dave is looking to override the base branch for a User Story to have it created from UAT rather than the default branch. When working with version control systems, such as Git, the convention is that the master branch is the default base for new feature branches. However, the correct answer to where one can find and possibly override the base branch for a feature branch is (c) In the Project linked to the User Story. Typically, this option is available within the settings or branch management area of the repository hosting service or the project management tool that integrates with it.
If this functionality is supported, Dave will be able to select UAT as the base when creating a new branch for the user story. Otherwise, this might be a manual process where Dave will need to ensure that the local repository is switched to the UAT branch before branching off to ensure the new feature branch tracks UAT instead of master.