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
Keshan disease is caused due to deficiency of: 
Select and explain. 
A. Selenium, B. Chromium, C. Iodine, D. Iron
A: Selenium
Answer: A: Selenium 
Explanation: Keshan disease is an endemic cardiomyopathy found in children and young women residing in regions of China where dietary intake of selenium is low ( Ref: Harrison's principle of internal medicine 17th edition, chapter 71.