Final answer:
The hypothalamus (option C) in the brain is the primary region responsible for controlling body temperature, acting like a thermostat to either cool down or heat up the body as necessary.
Step-by-step explanation:
The area of the brain that provides the primary control of body temperature is the hypothalamus. The hypothalamus acts as a thermostat and regulates the body's core temperature through various processes. When body temperature rises above the set point, the hypothalamus can initiate cooling mechanisms such as increasing blood circulation to the skin's surface and starting the sweating process, which allows heat to dissipate through evaporation.
Conversely, if the body temperature drops below the threshold, it causes shivering to generate heat and increases heat production through the action of thyroid hormones. Therefore, the correct answer to the question is C. hypothalamus.