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

Which of the following classes is one valid superclass of 'sieve tube'?

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

Answer: phloem