Answer: D. It can melt to a depth of a few meters in summer, then refreeze in winter.
Explanation:
Permafrost is ground which remains frozen for two or more years. Permafrost consists of soil, rock and sand fused together by ice. Mostly found in areas in high altitude, the Arctic, Antarctica, it is common in periglacial environments where temperatures are below freezing
.
The topmost layer of permafrost can melt in summer and refreeze in winter. This thawing and refreezing produces a ground pattern called columnar joints similar to the one formed when molten lava cools.
The massive rain forest is one of the major barriers to travel in the Congo region. The correct option among all the options that are given in the question is option "c". This rain forest is very dense in some places and it is almost impossible to pass through it. I hope the answer helps you.
