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: Pathology
Confirmation of myelofibrosis is by ? 
Select and explain. 
A. Bone marrow aspiration, B. Peripheral smear, C. Leuocytes alkaline, D. Bone marrow biopsy
D: Bone marrow biopsy
Answer: D: Bone marrow biopsy 
Explanation: Ans. is `d' i.e., Bone marrow biopsy Bone marrow biopsy is essential for diagnosis