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

The property 'was performed by' applies to instances of 'process', and 'physical process' is a subclass of 'process'. Which class can appear as the value of 'was performed by' for instances of 'physical process'?

A. stratopause
B. agent
C. ice surface
D. molecular neutral number density

Answer: agent