This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pharmacology
Lubipristone is a 
Select and explain. 
A. Enkephalinase inhibitor, B. Guanylyl cyclase agonist, C. Chloride channel activator, D. 5HT4 agonist
C: Chloride channel activator
Answer: C: Chloride channel activator 
Explanation: Lubipristone is a chloride channel activator used in treatment of IBS (Irritable bowel syndrome) with constipation.