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
Essential WHO criteria for polycythemia vera? 
Select and explain. 
A. Tyrosine kinase JAK2 V617F and other mutations, B. Low levels of erythropoietin levels, C. Thrombocytosis, D. Increased MCV
A: Tyrosine kinase JAK2 V617F and other mutations
Answer: A: Tyrosine kinase JAK2 V617F and other mutations 
Explanation: None