This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: All India exam, Subject name: Medicine
Which one of the following drugs is the most common cause of progressive multifocal leukoencephalopathy? 
Select and explain. 
A. Natalizumab, B. Cituximab, C. Rituximab, D. Bevacizumab
A: Natalizumab
Answer: A: Natalizumab 
Explanation: Causes of progressive multifocal leukoencephalopathy:AIDSHematological malignanciesTransplant recipientsChronic inflammatory diseasesNatalizumab, a humanized monoclonal antibody(ref:Harrison's 18/e p3427)