Task: Class Definition Understanding (ontology: Arts_Media_Entertainment/Propp)

Which of the following best defines 'ATU Types' ?

A. The version identifier of the ATU ontology
B. The set of all terminal (leaf) nodes in the ATU hierarchy
C. Bibliographic details of published folktale collections
D. Objects that cannot be counted or measured quantitatively

Answer: The set of all terminal (leaf) nodes in the ATU hierarchy