To create a join in a data source that already uses relationships, the associate must double-click a logical table in the canvas, making C correct. Tableau's data model has two layers. The top-level logical layer contains logical tables connected by relationships. A join cannot be created directly between these logical tables because joins operate in the underlying physical layer. Double-clicking a logical table opens its physical Join/Union canvas. From there, the associate can drag or double-click additional physical tables and define the required join clauses and join type. This distinction is fundamental to Tableau's modern data model. Relationships connect logical tables while keeping them separate and preserving their natural level of detail. Joins merge physical tables into one logical table using an explicitly defined join configuration. Selecting Add in the Connections pane adds another connection; it does not itself create the join. Dragging a table directly onto the top-level logical canvas generally creates a relationship rather than a physical join. Double-clicking a table in the Tables pane is not the step used to enter the physical layer of an existing logical table. Tableau's official documentation explicitly instructs users to double-click a logical table to open the physical layer where joins and unions can be created.