Task: Class Relation Understanding (ontology: Sciences/Biology)

Which of the following classes is one valid superclass of 'ossicle'?

A. ADP-ribosyl cyclase/cyclic ADP-ribose hydrolase 1 (human)
B. B-cell receptor CD22 (mouse)
C. C-C chemokine receptor type 1 (human)
D. skeletal element

Answer: skeletal element