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In Lightning Web Components (LWC), a reactive variable is a variable that, when changed, automatically updates the rendered DOM. To create a reactive variable, it is necessary to define the variable directly within the component class. This allows the template to reference the variable, and any changes to its value will propagate to the user interface, triggering a re-render of the affected elements.

When defined properly, this behavior is enabled by the LWC reactivity system, which tracks changes to component properties. Using reactive variables enhances the interactivity and responsiveness of the component, as the UI is updated in real time without requiring additional function calls to refresh the view.

The other options lack the necessary context or procedures to establish this reactivity. For example, exporting a variable from the module does not inherently make it reactive; it must be included in the component class context. Importing a variable from another module would not establish a link with the component’s rendering lifecycle. Creating a global variable, while technically possible, does not leverage the LWC framework’s reactivity features and is not a recommended practice in component-based architecture.