Assertion : Small sized animals are rarely found in polar regions.
Reason : Small sized animals have larger surface area relative to their volume and they have to spend much energy to generate body heat through metabolism.

Answer

A

Explanation

Thermoregulation is an energetically expensive process for many organisms. Heat loss or heat gain is a function of surface area. Small sized animals (such as shrews, humming birds etc.), have a larger surface area relative to their volume, they tend to lose body heat very fast when it is cold outside, thus they have to expend much energy to generate body heat through metabolism. This is the main reason why very small animals are rarely found in polar regoins.