List and explain the two sub-regions of frigid zone

The two sub-regions of the frigid zone are North Frigid Zone and South Frigid Zone.

Explanation:

Earth is divided into five geographic zones, one torrid zone, two temperate zones, and two frigid zones. The two frigid zones are the ones that are occupying the northernmost and southernmost parts of Earth. The area that they occupy more specifically is between 66°33' N and 90° N, and 66°33' S and 90° S.

These two frigid zones are the coldest zones on Earth. The north one is dominated mostly by the frozen Northern ocean, while the south one is mostly dominated by continental mass covered with thick ice. These zones are unique in that they have constant sunlight at their furthest parts for half a year, and after that constant night for half a year. The sunlight falls at such a sharp angle that the rays disperse over a very large area and don't heat up the surface properly, resulting in ice sheets and glaciers.

a and b because with the other three, they simplify to something else.