This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: C.N.S, Subject name: Medicine
[{'content': 'Floppy iris syndrome is associated with usage of \nSelect and explain. \nA. Anticholinergics, B. PDE- 5 inhibitor, C. Selective alpha- adrenergic antagonist, D. 5 alpha reductase inhibitor', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Selective alpha- adrenergic antagonist side effects may include hypotension, dizziness, nasal congestion, headache, and floppy iris syndrome. Ref Harrison 20th edi page no 2833', 'role': 'assistant'}]