Final answer:
The comfortable temperature range when the body is at rest and in an environment of 50% humidity with slight air movement is option C, 80 °F, which is close to the thermoneutral temperature.
Step-by-step explanation:
The question pertains to the comfortable temperature range for the human body when it is at rest in specific environmental conditions. Considering the information provided, the thermoneutral external temperature, which is the temperature at which the body does not need to expend energy for thermoregulation, is about 84 °F. This is closer to option C, which is 80 °F, where the body is near the state of comfort without significant expenditure of energy to maintain its core temperature, which remains steady at around 36.5-37.5 °C (or 97.7-99.5 °F).