Which widget can be used to select associated objects when multiple selections are possible?

The reference set selector is the correct choice for selecting associated objects when multiple selections are allowed. This widget is specifically designed to handle many-to-many relationships within Mendix applications, enabling users to select several objects from a reference set effectively. It displays a list of available associated objects and supports the selection of multiple items, making it ideal for scenarios where you want users to specify several related entities.

In contrast, other options may not accommodate multiple selections in the same manner. The dropdown selector is typically used for single selections, limiting the user's choice to one item at a time. The object list can also fall short for multi-selection tasks, depending on its configuration. Meanwhile, the multi-select box does allow for selecting multiple options but is not optimized for handling complex relationships in the way that the reference set selector is. Hence, the reference set selector stands out as the best fit for selecting multiple associated objects in Mendix.