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: Social & Preventive Medicine
All of the following are continuous variable   except 
Select and explain. 
A. Weight in kgs, B. Height in cm, C. Hb levels in mg/dl, D. Human blood group
D: Human blood group
Answer: D: Human blood group 
Explanation: Human blood group (A,B,AB,O) is a type of discrete variale.