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

Which of the following definitions best describes 'median external naris'?

A. The the concept is a portion of the nephron through which water flows, moving passively down its concentration gradient.
B. An organelle found in cnidoblast (nematoblast) cells. When matured, these stinging organelles store toxins and can deliver them when the cnidocil (a short extension of the the concept) is stimulated by a prey or another stimulus.
C. Am unpaired external naris that lies in the midline of the head.
D. The process whose specific outcome is the progression of a sinoatrial (SA) node cell over time, from its formation to the mature state. SA node cells are pacemaker cells that are found in the sinoatrial node.

Answer: Am unpaired external naris that lies in the midline of the head.