Final answer:
The primary mechanism for maintaining homeostasis in the body is a negative feedback loop (option A), which regulates bodily functions by reversing changes that move away from a set normal range.
Step-by-step explanation:
The primary mechanism for maintaining homeostasis in the body is through a negative feedback loop. This system responds to changes by activating mechanisms that reverse those changes, thereby keeping body functions within a set normal range. Negative feedback loops involve a stimulus, sensor, control center, and effector that work together to regulate critical bodily functions such as body temperature and blood glucose levels. While positive feedback loops also exist and play roles in certain processes, negative feedback is the predominant mechanism for homeostasis.