Question

What is permafrost?

Answer 1

Permafrost is a thick subsurface layer of soil that remains frozen throughout the year, occurring chiefly in polar regions.

I believe it would be D.

Answer 2

Answer: d. the upper part of the ground that remains frozen throughout the year

Explanation: Permafrost covers large portions of the Earth crust with almost a quarter of the land area in the Northern Hemisphere having permafrost underneath them. Permafrost is defined as a combination of soil, rocks and sand held together by ice remaining frozen all year long (though the active layer at the top doesn't always stay frozen. This layer is the active layer).