C
Below is a question with multiple-choice answers. Choose the correct option based on your reasoning.

### Question:
The fur color of a bear varies with its environment. Polar bears found in the Arctic have white fur, while black bears found in Pennsylvania have dark fur. Which best describes the variation of fur color amongst the bear species?

### Choices:
A. modified characteristic
B. ecological succession
C. structural adaptation
D. selective breeding

### Answer:
