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
Atrial fibrillation is common in: 
Select and explain. 
A. Adrenogenital syndrome, B. Addison's disease, C. Hyperthyroidism, D. Von-Willebrand's disease
C: Hyperthyroidism
Answer: C: Hyperthyroidism 
Explanation: None