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: Medicine
Drug used in irritable bowel syndrome with constipation 
Select and explain. 
A. Lubiprostone, B. Fedotozine, C. Loperamide, D. Mebeverine
A: Lubiprostone
Answer: A: Lubiprostone 
Explanation: Lubiprostone (CL- channel activator).