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

Which of the following definitions best describes 'air mass'?

A. A mass of gas which is separated from its surroundings by either 1) a thin liquid layer or 2) a physical or compositional discontinuity.
B. The concentration of europium when measured in water ice.
C. An object which is composed of a continuous mass of air.
D. An air mass which is part of the free atmosphere, including the troposphere and stratosphere.

Answer: An object which is composed of a continuous mass of air.