Final answer:
The example of a unit-level activity is d. Assembling products, which must be done for each individual unit that is produced.
Step-by-step explanation:
An example of a unit-level activity would be d. Assembling products. Unit-level activities refer to tasks and actions that are performed for each unit or piece of good produced by a company. These activities are directly associated with the production volume and occur every time a new unit is created. Assembling products is a clear illustration of this, as the activity is required for the completion of each individual unit. Other examples of unit-level activities might include installing parts or performing product-specific tests, as each of these is necessary for every single unit produced.
Activities such as heating a manufacturing facility (a) or advertising products (c) are not unit-level activities, as they are not directly tied to the production of each individual unit. Setting up machines (b), while necessary for production, is typically not performed for each unit and is instead usually a batch-level activity.