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
A 59-year-old male came with Hb 18.0 gm/dl on three occasions. The resident doctor wants to exclude Polycythemia Vera. Which of the following is the most relevant investigation - 
Select and explain. 
A. Hematocrit, B. Total leukocyte count, C. Red cell mass, D. Reticulocyte count
C: Red cell mass
Answer: C: Red cell mass 
Explanation: None