Final answer:
Positive feedback systems increase the intensity of the response to a stimulus. The correct answer is 'a) Enhanced and increases', as such systems amplify the initial stimulus in processes like childbirth and milk production in nursing mothers.
Step-by-step explanation:
Positive feedback systems operate by enhancing the initial stimulus, making it stronger. An example of positive feedback is the process of childbirth, where the contractions of labor increase in response to the baby descending in the birth canal. Similarly, milk production in nursing mothers is regulated by a positive feedback loop; the more the baby suckles, the more prolactin hormone is released, which in turn promotes more milk production. These mechanisms are designed to amplify the response until an end goal is reached.
Therefore, the correct answer to the question is 'a) Enhanced and increases', as positive feedback mechanisms increase the activity of the system in response to a stimulus, rather than shutting it off or reducing it.