Which scenario best illustrates an internal stimulus?

An internal stimulus is a cue that originates from within an organism, prompting a certain behavior or response. In the scenario where a child drinks milk from a bottle when she is hungry, the internal stimulus is the sensation of hunger. This need arises from the body's requirement for nourishment, and the behavior of drinking milk is a direct response to that internal cue.

Hunger is a physiological state that signals to the child that it is time to eat. The act of seeking milk is motivated by this internal drive, making it a clear illustration of how the body communicates its needs and how the individual responds to it. In contrast, the other scenarios involve responses to external stimuli, such as temperature, visual cues, or auditory signals, rather than internal needs.