A penguin's feet are nearly as cold as ice, while the bird's core body temperature is much higher. Which of the following explains this observation?
1) Penguins have a unique circulatory system that keeps their feet cold.
2) Penguins have a thick layer of blubber on their feet to insulate them from the cold.
3) Penguins have a high metabolic rate that generates heat in their core body.
4) Penguins have a specialized heat exchange system in their feet.