Tundra biomes are found in the northern polar region. The ground is frozen from deep underground nearly to the surface. The thin layer of soil allows only small plants with shallow roots to grow. However, it is believed that global warming might cause tundra ground to thaw to a greater depth, allowing larger plants to grow. If this occurs, animal populations in the tundra could be expected to increase. Which BEST explains why animal populations could increase?

A. An ecologically warmer habitat would increase oxygen rates.

B. Nutrients would cycle more quickly to decomposers.

C. Territory would increase in size.

D. A limiting factor would become more available