Task: Class Definition Understanding (ontology: Earth_Environment/EnvironmentOntology)

Which of the following definitions best describes 'active layer in a cryosphere'?

A. A layer which is composed of ground that 1) remains unfrozen due to increased solute concentration and 2) is present within a mass of permafrost.
B. A layer which is composed of ground that is 1) subject to annual thawing and freezing and 2) present in areas underlain by permafrost.
C. A layer of environmental material which is subject to freeze-thaw cycles.
D. A cryospheric layer which is primarily composed of snow.

Answer: A layer of environmental material which is subject to freeze-thaw cycles.