Answer: Option (C)
Explanation: The modern plant life that existed in the paleocene epoch were the temperate forests, that came up soon after the cretaceous-tertiary mass extinction, at about 62-65 million years back, which is marked as the K-T boundary.
The temperate forest covers the region from the tropics to about 60-70° latitudes in both the hemisphere. This region is rich in deciduous forest and contains a large amount of humidity, high precipitation level and rich in plant as well as animal bio-diversities. A huge number of plant species evolved since then.
Thus, the region during the paleocene epoch helped in the expansion of variable species by providing necessary conditions for their growth and development.
Hence, the correct answer is option (C).