This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Virology, Subject name: Microbiology
Which of the following clinical specimen for detection of BK polyomavirus by electron microscopy? 
Select and explain. 
A. Brain tissues, B. Urine, C. Blood, D. None of the above
B: Urine
Answer: B: Urine 
Explanation: Ans. is 'b' i.e., Urine (Ref: Dr D.R. Arora, 3rd/e, p. 552)* BK virus was isolated from urine of a renal transplant recipient, causes subclinical infection of children before the age of 10; virus persists for throughout life in kidneys. Reactivation may occur in last trimester of pregnancy and following immunosuppression for organ transplantation.