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

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

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

Answer: Unit