This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Uveal Tract, Subject name: Ophthalmology
Which of the following is the most common cause of anterior uveitis? 
Select and explain. 
A. Idiopathic, B. HLA-B27, C. Sarcoidosis, D. Tuberculosis
A: Idiopathic
Answer: A: Idiopathic 
Explanation: Ans. (a) IdiopathicRef: Yanoff 2/e, p 1115, Review of ophthalmology by William B. Trattler, peter K. Kaiser, Neil J. Friendman 2012, p 299, Esentials of ophthalmology by Neil J. Friedman 1st 2007, p 195