What is the most important abiotic factor that
limits distribution of the tundra biome?

Temperature is the most harsh abiotic factor that limits distribution of the tundra biome.

Explanation:

The tundra biome can be described as a biome that is one of the most abundant biome of the earth but allows little growth of trees due to its very cold temperatures. Often, in a tundra biome, no trees would be seen. The ground soil of this biome remains frozen most of the year and is termed as permafrost. The tundra biome shows very little biodiversity due to the extreme cold conditions. Very few animals and plants are adapted to live in these conditions.

the answer is d.) homologous; have mammary glands