Choices: [+] They have cold blood. [+] protect them. [+] They eat a lot. [+] hard outer covering. [+] by indirect light. [+] They go swimming. [+] They have thick fur. [+] When it's cold.
Given those answer options, answer the question: Fact 1: Some animals' fur grows thicker for staying warm in the winter. Fact 2: Polar bears grow fur to survive in the cold. Given the two facts above, how do polar bears stay warm in the winter?
A:
They have thick fur