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

The property 'has source unit' applies to instances of 'Unit Conversion', and 'AngstromToMeter' is a subclass of 'Unit Conversion'. Which class can appear as the value of 'has source unit' for instances of 'AngstromToMeter'?

A. Characteristic
B. Measured Characteristic
C. Observation
D. Unit

Answer: Unit