Task: Property Constraint Reasoning (ontology: Earth_Environment/EnvironmentOntology)

The property 'produced by' applies to instances of 'material entity', and 'subatomic particle' is a subclass of 'material entity'. Which class can appear as the value of 'produced by' for instances of 'subatomic particle'?

A. material entity
B. transient tracer
C. surfactant
D. ligand

Answer: material entity