As you have observed, animal hairs usually have a large medulla composed of air-filled compartments. These air-filled compartments are present for a reason and can actually help hair do its job better. Describe one reason that might explain why having a hair made of air filled compartments could be helpful to an animal. PLEASE HELP

to provide insulation

Explanation:

The medullary index is the proportion of the diameter of the hair medulla in regard to the diameter of the entire hair: The equation to calculate the medullary index is medulla diameter/hair diameter. In animals, the hair medulla is generally thicker compared to humans (medullary index approximately 0.5 and 0.33, respectively). The thicker the diameter of the hair medulla, the better is the insulation.

correct answer is a. and d.