What does permafrost mean?
a. the land is permanently frozen
b. the water is permanently frozen
c. the lower layer under the ground is permanently frozen
d. the lower layer under the ground is not frozen

The correct answer is C. The lower layer under the ground is permanently frozen

Explanation:

"Permafrost" is a term used to refer to a lower layer under the ground in some biomes that is permanently frozen or has a temperature under 0°C, this involves the formation of ice in some cases. Additionally, permafrost is common in biomes such as the tundra that are located at high elevations or near the poles where the temperature is quite low. Besides this, the existence of permafrost creates conditions under which only specific species of animals and plants can survive. According to this, permafrost means that the lower layer under the ground is permanently frozen.

credit card number 4 is the right answer