Task: Class Relation Understanding (ontology: Food_Agriculture/PlantOntology)

Which of the following classes is one valid superclass of 'petal spur'?

A. IE.03 3/4 of inflorescence emerged from flag leaf sheath stage
B. 4 root elongation stage
C. 2.02 main shoot and axillary shoots visible at two nodes stage
D. cardinal organ part

Answer: cardinal organ part