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:

Blubber is a thick layer of fat that provides excellent insulation, helping polar bears maintain a constant internal temperature in cold - weather conditions. The other options are not the main adaptation for thermal homeostasis. Three layers of fur help but not as significantly as blubber. Finding shade underground is not typical for polar bears in their cold, icy habitat. White skin is for camouflage rather than thermal regulation.

Answer:

blubber