What structure allows developers to see and fine-tune the screen structure?

The Widget Tree is the correct answer because it provides a hierarchical representation of all the visual components (widgets) present on a screen in an OutSystems application. It allows developers to visualize the relationships between different widgets, making it easier to understand how they are organized and how they interact with one another.

By using the Widget Tree, developers can effectively manipulate the structure of the user interface, adjusting properties and methods of individual widgets directly within this visual context. This fine-tuning capability is essential for creating a well-structured and user-friendly application.

Although other options like Entity Structure, Screen Layout, and Navigation Flow are important in the development process, they serve different purposes. The Entity Structure focuses on the data models and their relationships, while Screen Layout deals with the arrangement of the entire screen but does not provide a detailed widget hierarchy. Navigation Flow represents the paths a user can take within the application, which is crucial for planning user experience but does not directly allow for fine-tuning the screen structure like the Widget Tree does.