Final answer:
The behavior of a squirrel collecting nuts for a food source is regulated by external stimuli and can be viewed as a chained behavior.
Step-by-step explanation:
The correct answer is C) Chained behavior; external stimuli.
In this scenario, a squirrel collecting nuts for a food source can be viewed as a behavior that is regulated by external stimuli. The squirrel's behavior of collecting nuts is a chained behavior, meaning it involves a sequence of actions that are linked together.
The external stimuli in this case include cues from the squirrel's environment, such as the sight or smell of nuts, which trigger the behavior of collecting them as a food source.