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

Which of the following definitions best describes 'step pool'?

A. A stream pool which is formed as a result of high-gradient, steep streams where water cascades over a rock or woody snag.
B. An occluded front which is adjacent to a warm front 1) that is moving in the direction of the coldest air in the vicinity, 2) where the original cold front is forced aloft at the warm front surface, and 3) where the coldest air is replaced by less cold air at the surface of the astronomical body.
C. A marine current that generally occurs below the permanent thermocline (where it occurs) or below 400 m depth and that is driven by density and temperature gradients.
D. One of the two elevated edges of the neural groove[GO,MP].

Answer: A stream pool which is formed as a result of high-gradient, steep streams where water cascades over a rock or woody snag.