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

Which of the following definitions best describes 'trough'?

A. An extraction fault with no discernible displacement within the fault plane.
B. The state of a layer of unsaturated air when its lapse rate of temperature is less than the dry-adiabatic lapse rate but greater than the moist-adiabatic lapse rate.
C. In meteorology, an elongated area of relatively low atmospheric pressure; the opposite of a ridge.
D. The occurrence of air temperature below 0 C (32F) that kills annual vegetation without formation of frost crystals on surfaces. See freeze, dry freeze, hard freeze, light freeze.

Answer: In meteorology, an elongated area of relatively low atmospheric pressure; the opposite of a ridge.