Final answer:
The phenomenon in which adaptations to a new stimulus will no longer occur unless the stimulus is altered is known as a 'Plateau'. This happens because the body becomes accustomed to the stimulus over time and ceases to further adapt.
Step-by-step explanation:
When the body is exposed to a new stressor, it initially enters a stage of alarm. If the stressor remains, the body will enter a stage of resistance, adapting to the new stimulus. However, over time, if the stimulus does not change, the body's response to it will plateau, meaning that further adaptations will not occur unless the stimulus is altered. The correct term that describes this phenomenon is 'b) Plateau', wherein after a period of adaptation, progress or change halts because the body has become accustomed to the stimulus.
This concept is closely related to sensory adaptation, a psychological process observed when constant exposure to a particular stimulus result in a decreased response. In practical terms, this could relate to exercise routines, where a person may stop seeing progress (a plateau) if they do not increase the intensity or variability of their workouts. This concept is also relevant in the context of learning and memory, where ideas like extinction and spontaneous recovery illustrate changes in response patterns over time.