Question

which adaptation helps polar bears maintain a constant internal temperature (thermal homeostasis) in cold weather? three layers of fur blubber finding shade underground white skin

Explanation:

Polar bears have a thick layer of blubber under their skin. Blubber is a type of fat that acts as an insulator, reducing heat loss and helping them maintain a constant internal temperature in cold - Arctic environments. Their fur also helps, but blubber is more crucial for thermal homeostasis. Finding shade underground is not typical behavior for polar bears in their cold habitat, and white skin is mainly for camouflage rather than thermal regulation.

Answer:

blubber