The temperature of the human body

The correct answer is C. Core human body temperature is held near 37 °C (98.6 °F) through homeostasis, whatever the season. The hypothalamus acts as the body's thermostat. In cold weather it triggers shivering and vasoconstriction, and in hot weather it triggers sweating and vasodilation, so the internal temperature stays stable.

Why the other options fail:

• A and D: A fall or rise in core temperature with winter is not normal physiology. A drop signals hypothermia, and an unchecked rise signals fever or heatstroke.
• B: Sweating and evaporation cool the body in summer, so core temperature does not rise with ambient heat.

Core concept: thermoregulation and homeostasis, a standard topic in human physiology under Biology. For Mains, it links to heatwave health impacts, where the body's regulatory limits are exceeded.

Trap: Skin or surface temperature does vary with weather, but the question asks about core body temperature, which stays constant.