Fact 1: If an animal lives under ground then that animal will be protected from a wild fire. Fact 2: Marmots live in underground burrows. Given the two facts above, why are marmots protected from wild fire?

pick from the following.
1). They're in water.
2). an external framework.
3). water conservation.
4). hard outer covering.
5). They don't live near fire.
6). They're underground.
7). They're fireproof.
8). important habitats.
The answer is:
6).