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

Which of the following classes is one valid superclass of 'secondary xylem tracheary element'?

A. tracheary element
B. 2.01 main shoot and axillary shoots visible at one node stage
C. 2.04 main shoot and axillary shoots visible at four nodes stage
D. 2.03 main shoot and axillary shoots visible at three nodes stage

Answer: tracheary element